Colour Analysis for Elementary Operation Water Drop

Purpose: To determine if the water sample meets Canadian Drinking Water Guidelines for Colour. Testing will be done on Local community treated water. The Canadian Drinking Water Guidelines has an aesthetic objective of 15 TCU (True Colour Units) for drinking water; you will test and compare your result to see if it meets these guidelines.


  • 1 - Canadian Guideline Limit Sample for Colour (CGLS)

  • 3 - Large plastic test tubes

  • Piece of white paper


  1. Label the test tubes; Control, Canadian Guideline, and Local community sample.

  2. Pour the 50ml of Canadian Guideline Limit Sample into the Canadian Guideline test tube.

  3. Fill the Control test tube with the deionized water to the same level as the Canadian Guideline test tube.

  4. Fill the Sample test tube with Local community water to the same level as the Canadian Guideline test tube.

  5. Hold the Local community test tube side by side with the Control and Canadian Guideline tubes over a white piece of paper.

  6. View the test tubes from above: Is the colour of the Sample lighter or darker than the colour of the Canadian Guideline tube?

  7. Record the results.

Record Your Results

OWD Elementary Colour

If the water sample has a colour lighter or equal to that of the Canadian Guideline then it passes the Canadian Drinking Water Guideline for Colour. If the water sample is darker in colour than that of the Canadian Guideline, it fails the Canadian Drinking Water Guideline of 15 TCU (True Colour Units).

Safe Handling of Materials Caution must be taken at all times when handling any chemicals. Although this test is safe to use in any area, please be cautious with the materials supplied. 


Where does the colour of the water come from?

When water has a visible tint to it, it is usually due to the presence of decaying organic material or inorganic contaminants such as iron, copper, or manganese. Limits for colour in drinking water are usually set based on aesthetic considerations. The Canadian guidelines are set at 15 TCU (True Colour Units), as most people can easily detect colour exceeding this level. Generally, colour is classified into two types: true and apparent colour. The most common ca use of true colour is decaying organic material such as dead leaves and grass. This type of colour is usually found in surface water. Apparent colour is caused by inorganic materials, usually iron, copper or manganese. The true colour of water can be distinguished from the apparent colour by filtering the sample to remove the larger organic particles. The following are some frequent colours that may be detected in drinking water and their most common causes.

Colour: Red or Brown
Cause: Generally indicative of iron or manganese in water
Health Hazards/Other Problems: Stains sinks and discolours laundry

Colour: Yellow
Cause: Suspended organic particles
Health Hazards/Other Problems: No adverse health risks (unless chlorinated; see below)

Colour: Blue or Green
Cause: Generally due to copper in water supply or corrosion of copper pipes leading into water supply
Health Hazards/Other Problems: Can cause staining of fixtures and laundry; high contents of copper (30 ppm) can cause vomiting, diarrhea, and general gastrointestinal symptoms

Colour: Cloudy, White, or Foamy
Cause: Usually due to turbidity (finely divided particles in water, either organic or inorganic)
Health Hazards/Other Problems: No adverse health risks but can cause abrasions to pipes and staining of fixtures

What are the health risks associated with drinking coloured water?

Generally speaking, the colour in water does not pose any health risks. However, there are some exceptions. If the colour is due to a metal contaminant, such as copper, mild gastrointestinal symptoms may result. Therefore, Canadian guidelines stipulate certain recommended limits to many inorganic materials. Also, when chlorinated, any organic material that is present in the water can combine with the chlorine to form compounds called trihalomethanes (THMs). Chloroform is a common THM and is considered poten tially carcinogenic (cancer causing). Therefore THMs in drinking water supplies that are routinely chlorinated are closely monitored and also have recommended limits.

What do I do if my water exceeds colour limits?

Colour in water can easily be removed usi ng activated carbon filters (charcoal). However, these filters need to be replaced periodically to maintain colour absorption activity. In larger plants, a common treatment method called coagulation and sedimentation is used. This method utilizes alum and other chemicals to remove the materials that cause colouration of drinking water, before being pumped out to people’s homes.