Approximately 80 per cent of diseases in developing countries are caused by water that has not been treated to make it safe for drinking. Common diseases caused by untreated water are cholera and typhus.
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Fig. 22.3.4 A water treatment plant
The main stages of water treatment are:
Learn more about testing pH in Chemical World 13.2
1. Screening: water from lakes or rivers is passed through a wire mesh to remove floating material, such as rubbish and branches.
2. Settling: the water flows into large tanks, where a chemical called aluminium sulfate is added. This helps small particles clump together and settle to the bottom of the tanks.
3. Filtration: the water passes through beds of sand and gravel. Any remaining particles are removed. The water now looks clear but may still contain bacteria.
4. Chlorination: chlorine is added to the water to kill any harmful bacteria. A very small amount of chlorine is needed. It must be enough to kill bacteria but not enough that we can smell or taste it.
5. Fluoridation: flourine is added in some countries (including Ireland) to prevent tooth decay. Finally, the pH of the water is checked to make sure it is within an acceptable range (pH 7–8). Treated water is stored in reservoirs or water towers until it is needed.
Water charges in Ireland
The introduction of water charges in Ireland in 2014 caused a lot of debate. 1. List three reasons why some people are against water charges.
2. Ireland was one of the last countries in Europe to charge for water. List at least three reasons why most European governments think it is necessary to charge for water.
