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| Water purification |
Water purification, or drinking water treatment, is the process of removing contaminants from surface water or groundwater to make it safe and palatable for human consumption. A wide variety of technologies may be used, depending on the raw water source, contaminants present, standards to be met, and available finances.
Sources of Drinking Water
Water to be used in public or private water supplies can be drawn from a variety of sources. Different sources of raw water demand different treatment methods to render it fit for human consumption.
Deep groundwater - The water emerging from some deep groundwaters may have
fallen as rain many decades or even hundreds of years ago. Soil and rock layers
will have naturally filtered the groundwater to a high degree of clarity even
before it is pumped to the treatment plant. Such water may emerge as springs,
artesian springs, or may be extracted from boreholes or wells. Deep groundwater
is generally of very high bacteriological quality but may be rich in dissolved
solids especially carbonates and sulphates of calcium and magnesium. Depending
on the strata through which the water has flowed, other ions may also be present
including chloride, and bi-carbonate and there may be a requirement to reduce
the iron or manganese content of this water to make it pleasant for drinking,
cooking, and laundry use. Disinfection is also required. Where groundwater recharge
is practised, such groundwaters should be graded as being equivalent to lowland
surface waters for treatment purposes.
Shallow groundwaters - water emerging from shallow groundwaters are usually
abstracted from wells or boreholes and the bacteriological quality can be variable
depending on the nature of the catchment. A variety of soluble materials may
be present including potentially toxic metals such as copper or zinc. In parts
of Bangladesh, many shallow ground water sources are contaminated with unacceptably
high levels of arsenic.
Upland lakes and reservoirs - typically located in the headwaters of rivers
systems, upland reservoirs are usually sited above any human habitation and
may be surrounded by some form of protection zone to restrict the opportunities
for contamination. Bacteria and pathogen levels are usually low but some bacteria,
protozoa and algae will be present. Where upland are forested or are peaty,
humic acids can colour the water brown. Many upland sources have low pH which
requires adjustment before the water is put into supply.
Rivers, canals and low-land reservoirs - lowland surface waters will have a
significant bacterial load and may also contain algae, suspended solids and
a variety of dissolved constituents
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