Sources of Drinking Water

Water to be used for human consumption is drawn from different sources, and each source requires different treatment methods to make it safe.

Deep Groundwater
Deep groundwater which supplies wells and springs probably fell as rain decades or hundreds of years ago. Layers of soil and rock have naturally filtered the groundwater to a high degree of clarity. Deep groundwater is generally free of bacteria but rich in minerals, especially carbonates and sulphates of calcium and magnesium. Depending on the strata through which the water flowed, ions of chloride and bicarbonate may also be present. Iron or manganese may need to be removed to make well water taste pleasant for drinking and cooking and to prevent the staining of laundry. Disinfection is also required.

When groundwater recharging is done, the groundwater's should receive the same treatment as lowland surface waters.

Shallow Groundwater
Shallow groundwater's pumped from wells or boreholes vary in bacteriological quality depending on the catchments. They may contain a variety of soluble materials, including metals such as copper or zinc, which can be toxic in certain amounts. In parts of Bangladesh, for example, many shallow groundwater sources contain unsafe levels of arsenic.

Upland Lakes and Reservoirs
Upland reservoirs, located at the headwaters of river systems, are usually sited higher than human habitation and are protected to decrease the risk of contamination. While bacteria and other pathogen levels are usually low, some bacteria, protozoa, and algae will be present. If the area is forested or peaty, the acids in humus tend to color the water brown. Many upland water sources have a low pH that has to be adjusted before the water can be used.

Rivers, Canals, and Lowland Reservoirs
Lowland surface waters are heavily contaminated with bacteria and often algae, as well as suspended solids and a variety of dissolved substances.

Bankside Reservoirs
Manmade or bankside reservoirs are generally sited close to a river. Water is pumped from the river into the reservoir for treatment. In the reservoir, suspended materials quickly sink to the bottom and bacterial levels fall dramatically. With a bankside reservoir, it is possible to treat and use lowland river water containing pathogens, treated sewage water, and agricultural runoff. The reservoir also serves as an emergency backup source of water. If the river were to become too polluted to use, water could be pumped from the reservoir until the river could be cleaned up. One disadvantage is that bankside reservoirs need a large area of land next to the river. Another disadvantage is that in the summer they tend to support the growth of algae, which can reach explosive proportions. The algae may release unacceptable levels of toxins into the water.

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