3.13 WATER IN THE HOME
How pure is domestic water? The water we use at home is called domestic water. As we have observed, domestic water usually comes from lakes, rivers and wells or bore holes. It is sometimes stored in reservoirs and supplied through a system of pipes and taps. This water is not pure like distilled water. It may be contaminated by suspended solids, by solutes dissolved in it, and by tiny living organisms!
We can easily remove suspensions from domestic water by decantation or filtration. In a modern water supply system, the water is filtered at a water works before it is stored in local reservoirs.
Most domestic water contains a small amount of dissolved solutes. These come from the rocks and soil over which the water has flowed. Most of these solutes are harmless and do not need to be removed. If you fill a small plate with domestic water and leave it to evaporate in the sun, you will probably find that a small residue of solute remains. Unfortunately, substances that we use in modern agriculture and industry often contaminate water. Some of these substances are poisonous. If they dissolve in lakes or rivers, they make the water unfit for domestic use.
The water we obtain from lakes, rivers and wells sometimes contains tiny living organisms. These are too small to be seen by the naked eye and are called micro-organisms. Some of the larger micro-organisms can be seen using a school microscope. Instructions for doing this are given in the box on the right. The smallest of the micro-organisms are called bacteria and viruses. Some of these are harmless but some cause diseases. They are so small that they can only be seen with a very powerful microscope. They are not removed by ordinary filtration. In a modern water works, the micro-organisms that remain after filtration are killed by treating the water with a gas called chlorine. They can also be killed by boiling the water for several minutes.
Using domestic water. We need domestic water for drinking and preparing our food, and for keeping ourselves, our clothes and our surroundings clean.
The water we use for drinking and preparing food should be free from micro-organisms. If it has not been treated with chlorine at the town water works, it should be boiled for several minutes before it is used. This will help us to avoid diseases caused by bacteria in the water.
Washing tables and dishes, and ourselves and our clothes, with soap and water, also helps to keep us healthy. It washes away the dirt and food particles that bacteria like to live and grow on. We can also use disinfectants to kill these bacteria. Keeping clean to avoid disease is called hygiene. Another important use of water in modern homes is in the water closet toilet. This removes our wastes in a hygienic way. A water seal keeps the smells in and the flies out!
- 1. What is contamination? Describe three main groups of impurities that may contaminate water. How is water purified at a water works?
- 2. What are bacteria? List three ways of killing bacteria.
- 3. What is hygiene? List the advantages of a water closet toilet.
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