Water Pollution

Government guidelines for contaminant concentration levels

Health Canada Guidelines give a detailed description of many contaminants, as well as the allowable concentrations under Canadian law.

Chemical Contaminants like arsenic, mercury, and nitrates.
Biological Bacteria, viruses, protozoa and other living contaminants.
Radiation Radioactive wastes.

Things to consider when looking into a potential water quality problem:

Does your municipality use surface water, or ground water? - Surface water is oceans, lakes, streams, etc. Ground water is water far underground, usually in an aquifer . Surface water and ground water are treated differently, and susceptible to different environmental contaminants.

What water treatment process does your region use? - See below for the basic process of water treatment.

What type of contaminant are you worried about? Pollution can come in all different forms; dissolved gases, solids, water-soluble mixtures. This distinction can make a big difference.

Where is the possible contamination site in relation to the water treatment plant? Upstream, or downstream?

Waste Water

Possible Contaminants:

Organics - Any carbon-based compound which gets into the water. Can be natural products like food waste or manure, decay products, or synthetics like insecticides and herbicides.

Inorganic - Molecules which aren't based around carbon atoms. Some of the most problematic inorganics are ammonia and cyanide. As well as...

Metals - While technically inorganic, metals are usually classified separately. Metals can get into water by dissolving out of rocks, from industrial or sewage wastes, mine tailing ponds, or seeping through the ground from the surface to the water table below. Metals of significant concern are lead, cadmium, mercury, and aluminum.

Nitrates - Again, technically inorganic, but the sources and problems are different enough to warrant a new section. Usually comes from agricultural run-off because of the over-use of fertilizers, or seeping out of manure holding tanks. Higher nitrate levels in the water can trigger algal blooms by giving microorganisms in the water resources they need to grow.

Water Treatment Process - The Basics:

Primary Settling - Large chunks of debris are filtered out by a screen. The dirty water is then allowed to sit while heavy solid particles sink to the bottom and oily residues rise to the surface. The residues can then be skimmed off the surface.

Advanced Primary Treatment (optional) - the use of chemical coagulants to remove some remaining organic waste.

Secondary Treatment - Reduces the Biological Oxygen Demand in the waste water. Helps microorganisms in the water decompose organic pollutants.

Further BOD reduction - Using screens or chemical coagulants to remove even more biological waste

Disinfection - Makes the water safe to drink by killing bacteria and viruses in the water. Can come in a number of different forms. The most common are using chlorine, ozone, chlorine dioxide, or ultraviolet radiation.


Biological Oxygen Demand - "Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need.

Biological Oxygen Demand is a measure of the oxygen used by microorganisms to decompose this waste. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline." - Stevens Institute of Technology, 2009

All information was derived from - Bunce, N. Environmental Chemistry, Second Edition. University of Guelph. unless states otherwise.