About industrial wastewater

Industrial wastewater is the by-product from an industrial process that can contain contaminants. Special care must be taken to make sure this wastewater is treated and monitored to keep harmful contaminants out of our water.

The law

All discharges of wastewater to the natural environment are regulated under the Ontario Water Resources Act.

There are also regulations under the Environmental Protection Act covering 9 specific industrial sectors:

  1. electric power generation
  2. industrial minerals
  3. inorganic chemical
  4. iron and steel manufacturing
  5. metal casting
  6. metal mining
  7. organic chemical manufacturing
  8. petroleum
  9. pulp and paper

Source law

You can find the complete set of rules relating to these activities at:

You can also find the complete set of rules relating to effluent monitoring and limit regulations for each industrial sector at:


All industrial wastewater facilities must have an environmental compliance approval to:

  • establish a new wastewater treatment facility
  • use, operate, or change an existing facility

The environmental compliance approval normally imposes site-specific effluent limits and monitoring and reporting requirements for the operation of the facility.

If your facility is subject to 1 of the 9 industrial regulations, you must follow additional requirements.

Get an environmental compliance approval

Monitoring and reporting

Industrial facilities that discharge wastewater directly into Ontario’s lakes and rivers must:

  • sample
  • analyze
  • report the results to the ministry

If your facility is also regulated by 1 of the 9 industrial regulations, you must submit your results electronically using the Ministry of the Environment Wastewater System (MEWS) web application.

Sampling and analysis must be done according to the Protocol for the Sampling and Analysis of Industrial/Municipal Wastewater.

View: monitoring data on industrial wastewater