Sources of Drinking Water
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
naturally filter the groundwater to a high degree of clarity 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 (i.e., a low concentration of pathogenic bacteria
such as Campylobacter, Giardia or Cryptosporidium) 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. 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, it is equivalent to lowland surface waters for treatment
purposes.
Shallow groundwaters
Water emerging from shallow groundwaters is usually
abstracted from wells or boreholes. 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 zinc and copper. In parts of
Bangladesh, many shallow groundwater sources are contaminated with unacceptably
high levels of arsenic.
Upland lakes and reservoirs
Typically located in the headwaters of river
systems, upland reservoirs are usually sited above any human habitation and may
be surrounded by a protective zone to restrict the opportunities for
contamination. Bacteria and pathogen levels are usually low, but some bacteria,
protozoa or algae will be present. Where uplands are forested or peaty, humic
acids can colour the water. Many upland sources have low pH which require
adjustment.
Rivers, canals and low land reservoirs
Low land surface waters will have
a significant bacterial load and may also contain algae, suspended solids and a
variety of dissolved constituents.
Information source:
Wikipedia
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