Last Revision:
August 1996

Statement of principles 1.0

This guideline describes the position of the Ministry of Environment and Energy (MOEE) regarding the assessment of water supplies for developments on individual private wells. The Guideline is based on MOEE experience with development utilising individual wells, and reflects the need to ensure that future owners of lots or homes have a high probability of being able to obtain adequate quantities of potable water for domestic consumption over both the short and long term.

This guideline is presented for use with the understanding that the use of individual private wells has been justified by the municipality or the local planning authority. This justification includes an evaluation of alternative types of servicing. The Province encourages municipalities to plan for environmentally appropriate servicing infrastructures by undertaking comprehensive, large-scale assessment of groundwater and surface water resources(see the Provincial Policy Statement).

MOEE Guideline B-1-1, Water Management - Policies, Guidelines, Provincial Water Quality Objectives of the Ministry of Environment and Energy, is made under the authority of the Ontario Water Resources Act (OWRA). Guideline B-1-1 deals with the protection and enhancement of drinking water quality and describes the Provincial Water Quality Objectives (PWQOs) and the Ontario Drinking Water Objectives (ODWOs). The primary purpose of Guideline B-1-1 is to protect public health and encourage the provision of aesthetically pleasing water. Water intended for human consumption should not contain any disease-causing organisms or hazardous concentrations of toxic chemicals or radioactive substances. Aesthetic considerations also provide a basis for drinking water objectives since the water should be pleasant to drink.

Although MOEE does not normally review development proposals consisting of five or fewer private residences, the Ministry recommends that supplies serving five or fewer private residences should use the ODWOs to ensure the quality of drinking water 1. This recommendation may apply to development by consent or at the official plan amendment stage in certain areas; contact the local MOEE Regional office for further information.

The Ontario Water Resources Act, RSO 1990, obliges the MOEE to comment on the quality of private water supplies which are part of development proposals submitted to the MOEE for review.

Ontario Regulation 903 establishes standards and regulations concerning well construction. With respect to proposals involving individual on-site sewage systems (subsurface sewage systems), a separate guideline for the assessment of the impact of such systems on adjacent lands is available from the MOEE office in your Region. The title of the Guideline is Technical Guideline for Individual On-site Sewage Systems: Water Quality Impact Risk Assessment.

With respect to communal water supply systems to serve more than five private residences, a Certificate of Approval, and possibly a Permit to Take Water will be required. For communal sewage systems, a Certificate of Approval will be required. For more information on communal systems, please contact the MOEE office in your area.

Objectives 2.0

The objectives of this guideline are as follows:

  • to provide technical guidance to professionals involved in land development (in particular, hydrogeologists) in the assessment of groundwater quality and quantity;
  • to provide an interpretation of the application of MOEE policy to development of individual private well water supplies; and
  • to ensure that development proposals are submitted with the required technical support.

Application 3.0

The guideline applies to all development proposals for residential development involving individual well water supplies. Development agreements between the proponent and the municipality, or its equivalent in unorganised areas, shall be used to bind development to the recommendations of approved hydrogeology studies.

The guideline also applies to developments for which a plan of condominium is required and to industrial, commercial or institutional developments where water is used for human consumption. Please contact your regional MOEE office for information on the applicability of the guideline to a particular development of this type.

Information requirements 4.0

4.1 General

A hydrogeological study will be required by MOEE prior to recommendation of draft approval for plans of subdivision and condominium, and may be required prior to approval of official plan amendments which would permit development on private services. The study must be performed and a report submitted to the MOEE at the time of circulation of the proposed official plan amendment or plan of subdivision. The report must address concerns relative to the following:

  • Future residents must be provided with water for domestic consumption that is of acceptable quality and of adequate quantity.
  • Appropriate well construction techniques must be followed in order to minimise the possibility of well water quality degradation.
  • There must be minimal adverse effects on well water in the development from sources of contamination on the site or on adjoining lands.
  • Developments must not result in water quantity interference conflicts between users in the development and users on the adjoining lands.

With respect to quality, each future domestic well must provide water that is safe and aesthetically suitable for human consumption. The suitability of the water for domestic use is determined by comparing the results of the analysis of ground water samples from test wells with the applicable ODWOs (see Section 4.4 and the Appendix).

With respect to quantity, each future domestic well must provide sufficient water for normal domestic purposes (see Section 4.3 "Well Water Quantity Testing"). This will be determined mainly on the basis of data from pumping tests in test wells.

After its initial review of a hydrogeological study report, the MOEE may advise the consultant and the proponent that additional information be supplied, or recommend that further work be done. The advice and recommendations must not be construed as conditions of approval but rather as suggestions for those cases where the proponent wishes to continue to pursue approval. Ultimately, it is the hydrogeology of the site itself which will determine whether a proposal is acceptable.

When a report is found to be incomplete, draft or preliminary, or makes unsubstantiated claims, the MOEE will advise the proponent by letter with regard to the report’s deficiencies. The MOEE may not undertake a full review until such time that a complete report(i.e., one which satisfies the requirements of this Guideline) has been submitted.

4.2 Test Well Requirements

Site assessment for water supplies from wells must be undertaken as follows:

  1. The minimum number of test wells will be:
    • 3 for sites up to 15 hectares in area;
    • 4 for more than 15 and up to 25 hectares;
    • 5 for more than 25 and up to 40 hectares;
    • for more than 40 hectares, one additional test well for each additional 20 hectares or portion thereof.

    Where development by severance is considered, determination of the availability of a potable water supply should be made as early as possible in the severance approval process.

    In areas where groundwater quantity or quality are considered marginal with respect to domestic requirements, as many as one test well per lot may be required;

  2. The areal distribution of test wells must be such that hydrogeological conditions across the site are adequately represented. Depending on the areal configuration and hydrogeological complexity of the site, more than the minimum number referred to in section i) may be required;
  3. Consideration must be given to past or present land uses. Existing improperly abandoned wells should be identified since they may impact on ground water. Moreover, any contaminant spills on or adjacent to the site which may affect water quantity or quality should be identified and evaluated for their impact on groundwater.

The test well(s) should be located in an area which would permit a proper assessment of these impacts;

  1. Test wells must be located and constructed in such a way as to permit the prediction of the quantity and quality of groundwater which domestic wells will supply in the future. Accordingly, the construction of these wells must be typical of wells which will be used in the development in the future, and must comply with Ontario Regulation 903, with the requirements of other jurisdictions, and with any additional specifications recommended by the consultant and/or MOEE.

Existing water wells located on the site or in the immediate proximity of the site may be used as test wells, provided they fulfil i) to iv) above, and are fully incorporated into the well water quantity and quality testing programs described in the sections below. The use of existing wells and of the data obtained from them must be justified in the report as being technically appropriate; however, there must be at least one test well, new or existing, located on the site.

If the consultant and licensed well contractor properly locate and construct the test wells, or if there are pre-existing wells on the property which meet the requirements of iv) above, the developer may use them later as domestic water wells. They must, however, yield potable water and meet the construction requirements indicated in the approved study recommendations, which are implemented by provisions in the development agreement between the municipality (or its administrative equivalent) and the proponent. If any such wells are not to be maintained for future use, they must be properly abandoned as required by Ontario Regulation 903; abandonment must be recommended in the hydrogeological study report and must be implemented by the development agreement. To ensure that the recommendations of the report are properly implemented, the consultant’s report may include recommendations for supervision of well construction by a qualified consultant at the time the well is being constructed by the (licensed) well contractor.

4.3 Well Water Quantity Testing

Each of the test wells must be subjected to a pumping test. The tests may be done sequentially, using the other wells as observation wells, or several wells could be pumped simultaneously. The report must contain all well logs, Water Well Records, raw pumping test data and graphs, and hydrogeological cross section(s), and must discuss the sustainability of domestic well yields, the potential for supply interference and site aquifer characteristics such as hydraulic gradient, transmissivity and boundary conditions.(Note that in most cases where on-site sewage systems are proposed, the impact assessment requires a determination of the hydraulic gradient.)

4.3.1 Pump Test Procedure

The following pumping test procedure is recommended:

  • the test wells should be fully developed prior to the pumping test in order to avoid unacceptable turbidity levels at the time of sampling;
  • the pumping test must begin with a static water level and must be performed at a fixed rate (±5%) for a minimum period of six hours 2 (longer where supplementary storage systems are necessary) of "continuous" pumping (no stoppages); water levels must be monitored in the test well and observation wells at an appropriate frequency; water must be discharged at an appropriate distance from the test wells to ensure that artificial recharge does not occur;
  • immediately following the pumping test, water level recovery must be monitored in the test wells until 95% recovery occurs or for 24 hours, whichever is less; where sufficient recovery does not occur, the issue of the long-term safe yield of the aquifer is especially significant and must be addressed; and
  • the test rate will be at least the minimum rate discussed below (also see Section 4.4.1.).

4.3.2 Calculation of Minimum Test Rate and Well Yield

The minimum pumping test rate and well yield required for a particular development must be calculated as follows:

The per-person requirement shall be 450 litres per day. Peak demand occurs for a period of 120 minutes each day 3. This is equivalent to a peak demand rate of 3.75 litres/minute for each person. The basic minimum pumping test rate is this rate multiplied by the "likely number of persons per well" which, for a single family residence, shall be the number of bedrooms plus one. Unless it is otherwise established to MOEE's satisfaction, a minimum of four bedrooms shall be used in the calculation. However, regardless of the results of this calculation, this rate shall not be less than 13.7 litres/minute.

The only instance where rates lower than these may be used is where preliminary results indicate that the pumping test rate cannot be sustained in the long term, and consideration is given to systems which would compensate for low well yields. In this case, the rate of test pumping may be decreased, but the duration must be proportionately increased such that the total amount pumped equals the amount that would have been pumped if the test had been conducted using the procedures and minima discussed above. The yield requirement must then be applied to the well and to the compensatory system on a daily basis. These systems and any special water treatment devices that may be necessary for their proper functioning must be fully described in the report.

Regardless of whether systems to compensate for low yields are required, the report must demonstrate that future domestic wells will sustain repeated pumping at the test rate and duration at 24hour intervals over the long-term.

Where a test well can safely provide water at the calculated rate, it is not acceptable to conduct pumping tests at low rates and subsequently recommend the use of systems to compensate for low well yields simply in order to limit the migration of poorer quality water into the well.

Consultants must provide a statement indicating that, in their professional opinion, the probable well yields determined on the basis of their investigations are representative of the yields which residents of the development are likely to obtain from their wells in the long term.

4.3.3 Additional Information

Shallow wells and unconfined aquifers are susceptible to seasonal fluctuations in water level. In these cases, the consultant must address this issue and may need to perform additional investigations to determine the possibility of future well water quantity problems.

Groundwater heat pumps which do not return water to the aquifer of origin are not permitted. If treatment systems which require additional amounts of water for their operation are to be used, those rates must be added.

Consultants should address the issue of whether the groundwater withdrawals in the proposed development and in other existing or planned developments in the area will exceed the long-term safe yield of the aquifer, or significantly decrease base flow to sensitive water courses (trout streams, etc.). Relevant information may be available from the local planning authority, other ministries and agencies, municipal offices, and local residents.

Where there is established development in the vicinity, information from residents and other sources regarding well yield problems(water shortages, replacement wells etc.) should be obtained.

4.4 Well Water Quality Testing

4.4.1 Raw Water Quality

The consultant must obtain and analyze sufficient water quality samples during each pumping test in order to determine the physical, chemical and bacteriological quality of the water. At least one of these samples must be collected during the last hour of the test. It is the consultant’s responsibility to address water quality changes over time and to demonstrate that the water quality data are representative of the quality of water which future residents can expect in the long term.

Prior to any testing for water quality, there must be no chlorine residual. Chlorine residual tests must be performed at the wellhead at the time that bacteriological samples are obtained, and must be reported.

Where there are wells in nearby established developments, information should be obtained from residents, where possible, and other sources regarding water quality problems. If on-site sewage systems are used in the existing development(s) and are also to be used in the proposed development, well water samples from the existing development should be obtained and analyzed. The consultant should use this information to predict the impact of the proposed on-site sewage systems on water quality within the proposed development.

Water quality may vary between aquifers or with depth in the same aquifer. The consultant should recommend appropriate well construction (see Section 4.5) and must comment on the potential for cross-contamination between aquifers.

Shallow and/or unconfined aquifers are susceptible to contamination from sources located at or near the ground surface. If wells are to be constructed within such aquifers, and especially where individual on-site sewage systems are also proposed, the consultant must address the risk of contamination and recommend measures which will reduce that risk.

The minimum set of parameters for which the analyses must be performed is listed in the Appendix, along with the applicable Ontario Drinking Water Objectives. Other parameters, such as heavy metals, pesticides, tannins, sulphide, phenols, and fluoride, maybe required by the Regional MOEE office in your area. Please contact the office for more information. The consultant must also determine whether conditions specific to the site or its surrounding area require the inclusion of additional parameters. Complete documentation of sampling times, any on-site analytical methods, and all analytical results must also be included in the report.

If methane or other potentially explosive gases are encountered during the water supply assessment, the consultant must make recommendations to adequately control this hazard.

Note: Where health-related ODWOs or treatment limits for aesthetic ODWOs have been exceeded, the areas which the relevant test wells represent may have to be excluded from the proposed development site. In this case a justification for the selection of the boundary of the site is required.

4.4.2 Treatment Systems

For some aesthetic parameters, the ODWOs may be exceeded provided that concentrations are below the treatment limits noted in Table 3. The Appendix lists these parameters, the limits for treatment and some comments on treatment methods. In cases where raw water sodium levels exceed 20 mg/L, warning clauses should be addressed to people on sodium restricted diets and should be registered on title. In addition, if water softening is utilised to reduce hardness, a warning should be registered on the title with are commendation that a separate tap, which by-passes the softener, be installed to supply unsoftened drinking water.

If the raw water from the wells exhibits values for aesthetic parameters that are above the ODWOs but below the treatment limits, or if supplemental storage systems are proposed which require special treatment systems, the municipality’s assent to development based on treatment systems must be obtained in the form of a Resolution of Council, prior to MOEE recommending draft approval(see Section 5.0 Implementation).

If treatment is required, "Comments on Treatment" listed in Table3 of the Appendix are provided for the purpose of assisting applicants and municipalities in deciding whether development based on treatment systems should proceed. Prior to the municipality considering approval of the development proposal and/or Official Plan Amendment, it is the applicant’s responsibility, based on advice from a qualified consultant, to satisfy the municipality that the concept of using treatment systems is appropriate. MOEE staff will not comment on the acceptability of the various proprietary treatment systems available.

The treatment systems mentioned in Table 3 of the Appendix are suggested for treatment for single parameters. When treatment for more than one parameter is required, the systems suggested may not be appropriate due to treatment process interferences. The consultant must supply recommendations regarding the type of treatment required.

4.5 Well Construction

Construction specifications for future domestic wells in the proposed development must be addressed by the consultant in the hydrogeological report. Minimally, the construction of both the test wells and future domestic wells must comply with Ontario Regulation 903 made under the Ontario Water Resources Act, and with municipal requirements - where applicable.

When on-site sewage systems are proposed, or when they already exist on adjacent property, protection of the wells from contamination by effluent must be addressed.

When shallow and/or unconfined aquifers are to be used, the consultant must recommend construction specifications and well locations to address the issue of the susceptibility of such aquifers to contamination from sources at or near the ground surface.

Water quality may vary between aquifers or with depth in the same aquifer. The consultant should recommend appropriate well construction, methods and requirements, and must comment on the potential for cross-contamination between aquifers.

The consultant or the MOEE may wish to recommend additional site-specific construction criteria and/or supervision of well construction by qualified staff. In studies in which the consultant’s initial findings show that water quality or quantity standards cannot be met without special well construction specifications, the initial data which led to these conclusions must be included in the report. The structure of the test wells on which the final quantity and quality data are based must meet these specifications and the wells must be tested according to the procedures stipulated in this Guideline, in order for the data to be deemed representative.

Subsections 13(2) and 13(3) of Ontario Regulation 903 require that wells be constructed such that the casing of a drilled well protrudes at least 30 centimetres above ground surface or above the floor of a well pit. Well water contamination caused by the entry at the well head of water originating at or near the surface may occur if the well head is buried. Subsection 20(3) requires that the well owner maintain the well in a manner sufficient to prevent such contamination. Where well heads are buried, locating, inspecting and servicing the well are difficult and expensive.

Subsections 13(2), 13(3) and 20(3) are often contravened when, after a well is constructed, contractors or residents bury the wellhead for reasons of convenience or aesthetics. Contractors and residents should be reminded of the intent and requirements of these portions of the Regulation, and of their responsibility to ensure that the finished grade of the ground surface allows the casing to protrude the required distance. This is necessary to prevent ponding at the well head or, in the case of well pits, prevents flooding of the pit. Where flowing well conditions occur, the requirements of Regulation 903 must be met.

4.6 Land and Water Use Conflicts

Land uses within a minimum of 500 metres of the site must be described. Where wells exist on or adjacent to the site, a survey of well owners, and sampling and analysis of representative well water, should be performed and reported. The potential for an adverse impact on the development must be addressed, when there have been, are, or may in the foreseeable future be significant potential sources of groundwater contamination (e.g., from old, operating or proposed waste disposal sites, road salt storage facilities, farming activities, locations of contaminant spills, etc.), or potential causes of quantity interference with groundwater resources or well water supplies (e.g., from municipal wells, dewatering activities, etc.) within a minimum of 500 metres of the site. The issue of whether additional water quality parameters should be included in the testing must also be addressed.

4.7 Phased Developments

Where a development application relates to an additional phase of a phased development, even though previous phases may already have been approved on the basis of previous hydrogeological studies which encompassed those phases or the entire site, a supplementary study and report is required. Water samples from wells that are located on nearby developed lots in previous phases that are in use and representative of the same formation, must be analyzed for the required parameters, and the well owners should be interviewed (where possible) regarding their experience with their well water quantity and quality. This information, as well as the Water Well Records and a map showing the locations of all wells in previous phases, must be provided. The original hydrogeological report must be re-assessed in light of the new information obtained and according to any new criteria or guidelines which may not have been in effect at the time of the original study. Where well water quality or well yield in the previous phases are not comparable to that found in the original test wells or predicted by the original hydrogeological study, the new study should investigate and explain the causes and provide new recommendations based on a re-assessment of the original report. Where new guidelines require information which is not included in the original report, the new report must provide it.

If the new phase does not contain test wells from the original study, new ones must be installed. Where additional study involving new test wells is necessary, most or all of the criteria set forth in this Guideline will apply. Consultants should discuss these issues with MOEE staff before proceeding.

Implementation 5.0

MOEE staff will implement this guideline through comments and advice supplied to municipalities, the public, and approval authorities on documents circulated under the Planning Act.

It should be noted that the MOEE will not recommend approval for official plan amendments and draft plans of subdivision or condominium unless the MOEE (or its agents) is satisfied that the hydrogeological report demonstrates that sufficient water is available. Where groundwater of adequate quality and quantity is demonstrated to be available to service the proposed development, the MOEE will require, as a condition of final approval, that the MOEE receive a copy of a fully executed subdivision or condominium agreement or other suitable development agreement between the municipality and the developer, which requires that the recommendations of the hydrogeological report as approved by the MOEE (or its agents) be implemented. The municipality should ensure that MOEE comments have been adequately addressed within the fully executed agreement.

If groundwater open loop heat pumps are being considered for use in the proposed development, they must be included in the hydrogeological study to ensure that domestic potable water supplies will not be adversely impacted. If the issue of groundwater heat pumps is not addressed in the report, MOEE will request that a condition be placed in the development agreement indicating that the use of groundwater heat pumps has not been approved as part of the development.

The possibility of using systems to compensate for low well yields(for example, controlled pumping to supplementary storage) is discussed earlier in this Guideline. However, while the MOEE may provide technical guidance, it is the municipality’s responsibility to decide whether development on the basis of such systems should be allowed. If the municipality agrees to their use, notification must be given through the development agreement between the municipality and the proponent(s). The municipality shares responsibility with the proponent(s) for ensuring that the terms of the development agreement are completed.

With respect to water quality, the following will apply (except for the 20 mg/L warning level for sodium):

  • Where health and aesthetic ODWO criteria are met, MOEE will comment favourably on approval of the Official Plan Amendment or on draft approval of the Plan of Subdivision or Condominium.
  • Where health-related ODWO criteria are not met, MOEE will recommend against approval of the proposal on the basis of individual wells.
  • Where health-related ODWO criteria are met but aesthetic objectives are exceeded, it may be possible to use in-home water treatment systems to reduce the values of the aesthetic parameter(s) concentrations to a level below the limits, and thereby meet the objectives.

This guideline lists concentrations considered treatable for several aesthetic parameters and some possible treatment systems(see Table 3 of the Appendix). However, it is the municipality’s responsibility to decide whether development on the basis of in-home treatment systems should be permitted. Following MOEE's review of a study which includes recommendations for such treatment, MOEE will notify the municipality (or its equivalent),the proponent, and the consultant that MOEE will only recommend draft approval following receipt of a Resolution of Council. The Resolution must advise that the municipality concurs with development based on use of these systems. The development agreement between the municipality and the proponent shall contain provisions for implementation of the recommendations, including treatment, in the approved hydrogeology study. The municipality shares responsibility with the proponent for ensuring that the terms of the development agreement are carried out.

Where health objectives are exceeded or where treatment limits for aesthetic objectives are exceeded, the local municipality and the approving authority should only consider development on the basis of a communal water system. MOEE approvals are required for Water Works for municipal and communal systems, as defined under the Ontario Water Resources Act and set out in MOEE Guideline B-14, Treatment Requirements for Municipal and Communal Water Works Using Groundwater Sources. The municipality shall assume ownership of and responsibility for the water works following completion.

Definition 6.0

Individual wells:
Private water wells supplying five or fewer residences (or the equivalent for other types of development) are referred to in this guideline as "individual wells".

Reference documents 7.0

Other documents that should be used in conjunction with this

Guideline include:

  • The Provincial Policy Statement, Ministry of Municipal Affairs & Housing;
  • "Technical Guideline for Individual On-Site Systems: Water Quality Impact Risk Assessment", MOEE.
  • "Water Management - Policies, Guidelines, Provincial Water Quality Objectives of the Ministry of Environment and Energy", MOEE Guideline B-1-1 (July 1994).
  • Ontario Water Resources Act, RSO 1990.
  • "Water Wells & Ground Water Supplies in Ontario", MOEE 1989.
  • Regulation 903, made under the Ontario Water Resources Act.
  • "Levels of Treatment for Municipal and Private Sewage Treatment Works Discharging to Surface Waters", MOEE Guideline F-5.
  • "Treatment Requirements for Municipal and Communal Water Works Using Groundwater Sources", MOEE Guideline B-14.

1 See "Ontario Drinking Water Objectives", Ontario Ministry of the Environment and Energy.

2 The minimum duration of six continuous hours incorporates safety factors with respect to seasonal variables.

3 Refer to page 5 of the MOEE publication entitled "Water Wells & Ground Water Supplies in Ontario", 1989. The per person daily demand used here is the upper limit of the estimated range.


Groundwater quality parameter tables

Published documents have been the main source of information regarding the water quality limits appearing in the tables below. Additional parameters may be required by the Regional MOEE office in your area. Also, when new water quality limits are formally instituted by the relevant authority, this guideline will be updated and an effort will be made to distribute the new requirements to interested parties. However, it is the responsibility of the consultant to apply those criteria which are appropriate at the time the study is performed and reported. It is, therefore, highly recommended that consultants maintain regular contact with the MOEE.

Table 1: Health-related bacteriological parameters
ParameterOntario Drinking Water Objective (See Note 1)Comments
Escherichia coli0Indicators of contamination
Fecal coliforms0Indicators of contamination
Total coliforms0Indicator of possible or potential contamination

Exceedances must be explained and any re-sampling must be fully documented with respect to chlorine residual, rates and duration of pumping, etc.

While the stated ODWO for Total Coliform is 0 counts per 100 ml of sample, it is recognized that the objective has been set as an indicator of inadequate disinfection within the distribution systems associated with water works. For private water wells not subject to approval under the OWRA, the MOEE and Health Units have historically used the limit of <5 counts per 100 ml in the absence of a chlorine residual as indicating acceptable water quality. For the purposes of the assessment described by this Guideline, Total Coliform counts of less than 6 per 100 ml of sample (and 0 for E. Coli and fecal coliforms) shall be considered as indicative of acceptable water quality.

The chlorine residual must be zero before any bacteriological sample can be taken.

Table 2: Health-related chemical and physical parameters
ParameterOntario Drinking Water Objective (See Note 2)Comments
Nitrate (as N)10.0 mg/Lcontamination indicator; exceedance may be dangerous to infants and others
Nitrite (as N)1.0 mg/Lcontamination indicator
Nitrate plus Nitrite (as N)10.0 mg/Lcontamination indicators
Sodium20 mg/L (see note 3)levels may be significant for persons with medical conditions requiring low salt diets
Turbidity1 NTU or 1 FTU (see note 4)could indicate problems in well construction or a naturally occurring problem; may interfere with water treatment
Other parameters(see note 5)n/a

Note 2. Except for sodium, the Ontario Drinking Water Objective for parameters in Table 2 are Maximum Acceptable Concentrations under the Ontario Drinking Water Objectives. Units of measure and, where required, conversion factors must be provided. For more information on the Objectives, refer to the MOEE publication entitled "Ontario Drinking Water Objectives".

Note 3. This health-related limit is a "warning level" only. Exceedance calls for a recommendation that the local Medical Officer of Health be notified in order to alert persons with relevant medical conditions. Sodium also has an Aesthetic Objective of 200 mg/L (see Table 3).

Note 4. NTU = Nephelometric turbidity unit; FTU = Formazin turbidity unit. These terms are interchangeable. NTU is the term used in the ODWOs. For the purposes of this guideline, the consultant must note that if turbidity is present, particular care must be taken during testing to ensure that the bacteria requirements of Table 1 are met.

Note 5. See also section 5.5.1: "Raw Water Quality", above, regarding the responsibilities of the proponent or consultant to add parameters where necessary; the consultant must also provide the relevant information on any drinking water quality limits, including those from other jurisdictions.

If water softening is used, a separate tap supplying unsoftened water should be used for drinking purposes.

Table 3: Common aesthetic, analytical and indicator parameters
ParameterGeneral CommentsOntario Drinking Water Objective (see note 6)Maximum Concentration considered reasonably treatableComments on Treatment
Alkalinityuseful analytical parametern/an/an/a
Ammoniacontamination indicatorsn/an/an/a
Background Bacteriacontamination indicatorsn/an/an/a
Calciumsee Hardnessn/an/an/a
Chlorideassociated with salt problems250 mg/L250 mg/Lnot considered reasonably treatable above the limit
Colourassociated with certain metals and organic substances5 TCU (True Colour Units)7 TCUcarbon filter treatment systems (see note 7)
Conductivityuseful analytical parametern/an/an/a
DOC (Dissolved Organic Carbon)taste, odour, colour, turbidity, precursor for harmful contaminants after chlorination5.0 mg/L (as C)10.0 mg/L (as C)carbon filter treatment systems
Hardnesstaste, encrustation and reaction with soap500 mg/L as CaCO3 (see note 7)n/awater softener (see note 8)
Ironmay cause staining of plumbing fixtures and laundry0.3 mg/Lup to 5.0 mg/Lwater softeners or manganese greensand filters
Ironmay cause staining of plumbing fixtures and laundry0.3 mg/L5.0 to 10.0 mg/Loxidation with filtration through proprietary filter media or chlorination followed by sand or multimedia filtration
Magnesiumsee Hardnessn/an/an/a
Manganesemay cause staining of plumbing fixtures and laundry0.05 mg/L1.0 mg/Lwater softeners or manganese greensand filters
pHassociated with corrosion or encrustation or contamination by other substances6.5 - 8.5n/an/a
Sodiumtaste200 mg/L (see note 9)200 mg/Lnot considered reasonably treatable above the limit
Sulphatelaxative500 mg/L500 mg/Lnot considered reasonably treatable above the limit
TDS (Total Dissolved Solids)corrosion or encrustation of metal fixtures or appliances; taste; must be measured independently of Conductivity; turbidity500 mg/Ln/arequires written rationale that corrosion, encrustation or taste problems will not occur
Turbidity5 NTU or 5 FTU (see note 10)5 NTU or 5 FTU5 NTU or 5 FTUn/a
Other parameters(see note 11)n/an/an/a

Note 6. Except for hardness, the drinking water quality limits in Table 3 are Aesthetic Objectives under the Ontario Drinking Water Objectives. Units of measure and, where required, conversion factors must be provided. For more information on the Objectives, refer to the MOEE publication entitled "Ontario Drinking Water Objectives".

Note 7. Higher, iron-related colour may be removed by manganese greensand treatment; however, the nature of the constituents causing excessive colour must be determined. See section 4.4.2: "Treatment Systems",above.

Note 8. Generally, water with a hardness value of more than 300 mg/l is considered "very hard". The Ontario Ministry of the Environment publication entitled "Ontario Drinking Water Objectives", states that waters with hardness "in excess of 500 mg/l are unacceptable for most domestic purposes". A maximum treatable value is not available.

Note 9. Sodium also has a health-related "warning level" of 20 mg/l (see Table2). Since water softening results in high sodium levels, a separate tap, which supplies unsoftened water, should be installed for drinkingpurposes.

Note 10. For the purposes of this guideline, the consultant must note that if turbidity is present, particular care must be taken during testing to ensure that the bacteria requirements of Table 1 are met.

Note 11. See also section 4.4.1: "Raw Water Quality", above, regarding the responsibilities of the proponent or consultant to add parameters where necessary; the consultant must also provide the relevant information on any water quality limits, including those from other jurisdictions.