water pollution experiment
Ref: W09

The plumbing system in most homes carries the water that has been used and is flushed or drained away to the sewage treatment works. In Cornwall the company responsible for supplying water and treating it after use is South West Water - click here to visit SWW website

Sometimes waste gets into the water cycle and cannot be treated by the water company because it enters a river or the sea directly. In this case water can become polluted and cause problems for plants and animals living in and near the water, and all the life that relies upon water to survive.

Here is an experiment for you to do that will help show how this happens.

For this experiment you will need:

• A glass jar half filled with tap water
• A couple of drops of car engine oil
• Some cotton wool
• Some washing-up liquid
• A pipette

Your glass jar half filled with tap water represents your local river. What is this river called? Look on an OS Explorer map to find out the name or look on the Cornwall Rivers map (B04k).

At the moment the river is not polluted and it could provide a home for many different animals if the other conditions around the river offer the right habitat for them. Aquatic invertebrates, birds, fish and mammals would not be an unlikely sight.

• Rub the unpolluted water between your fingers, remember what this feels like. Look closely at the surface of the water, remember how clear it is.

• Write down what the water felt and looked like.

• Now put a couple of drops of engine oil into the water. This represents someone putting oil directly into a river or dumping it in a place where it will find its way into a river, for example through fly tipping (W02).

Engine oil should be taken to a council rubbish site where it will be disposed of properly. You might have heard about oil spills caused by large ships off the coast of Britain and other parts of the world. This can cause a tremendous amount of suffering to sea birds, fish and other sea creatures not to mention the effect on animals that use the beaches where oil is washed ashore. For more information go to the Ocean Link website or Global Marine Oil Pollution website

• Using the pipette and the cotton wool you are going to try and carry out a ‘clean up’ operation to take out all of the oil from the water. You will have to be very careful in doing this. The oil will settle on top of the water after a few moments (why is this?) this will help you to remove it.

• Rub the water between your fingers after you have completed your ‘clean up’ operation. Does the water feel like it did before the oil was put into it or can you feel the oil in it? Can you see a film on the top of the water?

• Write down how the water feels and looks now.

• How might the oil affect the birds landing on the surface of the water?

Even if you have done a really careful job of cleaning up all the oil, there will still be some left in the water. Think about how difficult it would have been to remove any of the oil if the water had been flowing like in a river or if there had been waves and tides like in the sea!

Sometimes detergent is used to break up oil when there has been a spill.

• Add some washing up liquid into the water and feel the water. Keep on adding detergent until the water no longer feels oily. How much did you need to use? Compare this to the amount of oil that was put into the water.

The detergent might have broken down the power of the oil to create a film over the water and to coat plants and animals but it hasn’t made the oil go away and now there is detergent in the water as well!

• What affect might detergent have on the plant and animal life found in a river? (W05)

It is better to prevent pollution than try and clean it up after it has happened.

• Use your findings to create a poem about the way oil affects water and the plants and animals that live in watery habitats like ponds, lakes, rivers, streams and other wetland areas.

• You can send your poem to the Westcountry Rivers Trust (B05) and the best ones will appear on the website.