Colour Analysis for High School Operation Water Drop

Purpose: To determine if the water sample meets Canadian Drinking Water Guidelines for Colour, by doing a visual comparison of 4 different sources:

  • Urban Treated water

  • Rural (aboriginal and/or non- aboriginal community) treated water

  • Untreated raw source water

  • Local community treated water

The Canadian Drinking Water Guidelines has an aesthetic objective of 15 TCU (True Colour Units) for drinking water; you will see and compare the different water sources. The 15 TCU (True Colour Units) is the concentration of the Canadian Guideline sample.


  • 1 - 50ml tubes containing Canadian Guideline Limit Sample for Colour

  • 6 - Large plastic test tubes

  • Piece of white paper


  1. Label the test tubes with their number, and appropriate name; #1 Control, #2 Canadian Guideline, and #3, #4, #5, #6.

  2. Pour the 50ml of Canadian Guideline to the #2 test tube.

  3. Fill the #1 Control test tube with the deionized water to the same level as the # 2 test tube.

  4. Fill the #3 Sample test tube with sample water to the same level as the #2 Canadian Guideline test tube.

  5. Hold the #3 sample test tube between the #1 and #2 tubes over a white piece of paper.

  6. View the test tubes from above: Is the colour of the #3 Sample lighter or darker then the colour of the #2 Canadian Guideline sample?

  7. Record the results.

  8. Repeat steps 4-6 with the remaining samples (#4, 5, and 6).

Record Your Results

OWD Colour English High School

If the water sample has a colour lighter or equal to that of the Canadian Guideline test tube then it passes the Canadian Drinking Water Guideline for Colour. If the water sample is darker in colour than that of the Canadian Guideline tube, 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.

Visit the Safe Drinking Water Foundation website to learn more about issues affecting safe drinking water.


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 (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 cause 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 potentially 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 using activated carbon filters (charcoal). However, these filters need to be replaced periodically to maintain colour absorption activity. In larger treatment 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.