What are the techniques for assessing the purity of water?

Water purity can be assessed through physical examination, chemical analysis, and microbiological tests.

Physical examination is the first step in assessing the purity of water. This involves checking the colour, odour, and taste of the water. Pure water should be clear, odourless, and tasteless. Any deviation from these characteristics could indicate the presence of impurities. For instance, a yellowish colour might suggest the presence of iron, while a foul smell could indicate the presence of sulphur compounds.

Chemical analysis is another crucial technique for assessing water purity. This involves testing the water for various chemical parameters such as pH, hardness, alkalinity, and the presence of specific ions like nitrates, phosphates, and heavy metals. The pH of pure water should be around 7, indicating that it is neither acidic nor alkaline. Hardness and alkalinity tests measure the concentration of calcium and magnesium ions, and bicarbonate and carbonate ions respectively. High levels of these ions can affect the taste of water and its suitability for certain uses. Tests for specific ions help to detect harmful substances. For example, high levels of nitrates can be harmful to infants, while the presence of heavy metals like lead and mercury can be toxic.

Microbiological tests are also essential in assessing water purity. These tests check for the presence of harmful microorganisms like bacteria, viruses, and parasites. The most common test is for coliform bacteria, which are usually found in the faeces of warm-blooded animals and humans. Their presence in water indicates possible contamination with faecal matter, which can cause diseases like diarrhoea and dysentery. Other tests check for specific pathogens like E. coli, Salmonella, and Giardia.

In conclusion, assessing the purity of water involves a combination of physical examination, chemical analysis, and microbiological tests. Each of these techniques provides valuable information about the quality of the water and its suitability for different uses.