Improved Drinking-Water Supply Technologies

The water supply technologies we consider are those compatible with the MDG target of improving access to safe drinking-water in low-income communities. For operational purposes, the WHO/UNICEF Joint Monitoring Programme has defined drinking-water as the water used for normal domestic purposes, including consumption and hygiene, and has classified drinking-water sources as either ‘improved’ or

‘unimproved’ (WHO/UNICEF, 2010). Improved drinking-water sources are those that ‘by the nature of their construction adequately protect the source from outside contamination, in particular with faecal matter’. Technologies that use improved sources, which we call improved drinking-water supply technologies, are more likely to secure a supply of safe drinking-water and, therefore, to promote the achievement of the MDG drinking-water target.

Improved drinking-water supply technologies are:

• piped water into dwelling, yard or plot

• public tap or standpipe

• tube well or borehole

• protected dug well

• protected spring

• rainwater collection

Unimproved drinking-water supply technologies are:

• unprotected dug well

• unprotected spring

• cart with small tank/drum

• tanker truck

• surface water (river, dam, lake, pond, stream, canal, irrigation channel)

• bottled water when the household uses water from an unimproved source for cooking and personal hygiene

An overview of improved drinking-water supply technologies illustrated by drawings (WHO/UNICEF, 2006) is presented below.

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Basically, piped water to the household is the most sophisticated technology. The drinking-water is treated and piped through house connections or yard taps. Drinking-water flows under pressure using a pump from the storage tank, satisfying the flow requirement demanded by the consumers, thereby achieving the three objectives mentioned in section 3.2.

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A public tap or standpipe provides water from a groundwater source. The water that people get from a public tap or standpipe is shared by more than one household. A public tap or standpipe requires

a high level of water pressure. Generally, a public tap or standpipe is located in a public square, at a distance from the house. The average distance from user households influences water consumption, because of the laborious job of carrying of water.

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Tube well or borehole technology is designed for the abstraction of groundwater (either at a shallow or at a deep level) using a pump operated in a suction mode. The suction pump draws water from a free or confined aquifer by creating a vacuum in the suction pipe. Shallow and medium-depth boreholes can be fitted with hand pumps, but deep boreholes will generally require a power-driven pump.

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The dug well is a method of groundwater withdrawal in which a hole is dug in the ground to a depth below the groundwater level. Inflow into dug wells occurs as a result of the lowering of the water level in the well. Usually no special equipment or skills are required for the construction of a dug well.

Protection is recommended to prevent bacterial contamination. The upper part of the well lining and the space between the wall and soil should be properly sealed has shown in the above illustration.

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Depending on the geographical and geological layout groundwater may be forced from underground to the surface. Generally, spring water emerges under the pressure of gravity or artesian gushing.

With gravity, and depending on the water table, groundwater flows over an impervious layer onto the surface. With artesian gushing, groundwater flows upwards into the spring, and is forced under pressure to the surface. A protection chamber should be constructed around the spring, and the water should flow out of the chamber through a suitably placed pipe. The point at which the water emerges is a focus of pollution, thus digging a diversion ditch is highly recommended. Some spring sources may be highly polluted by soil organics, especially after heavy rains. In such cases, water requires local treatment, for example filtration and disinfection.

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In countries with considerable rainfall, rainwater is a potentially important source of water supply.

Protected ponds replenished by rainwater are the main source of water supply in coastal areas. The approach of collecting, storing and using rainwater is highly feasible, but needs to be developed through adopting appropriate technologies.

The surface of roofs is used as a discharge. The rainwater is collected and stored in the dwelling, and is treated at home prior to use. The advantages of rainwater collection are simplicity and low cost. The disadvantages include the variability of precipitation and the resulting lack of guaranteed continuous service.

Although improved water supply technologies are necessary to provide safe drinking-water to low-income communities, they may not be sufficient if applied to drinking-water sources of inadequate quality. In areas where the air is polluted, rainwater may be contaminated by toxic aerosols. Dangerous levels of chemicals, such as naturally-occurring arsenic and fluoride, may be found in groundwater aquifers. Surface water from streams or rivers can carry infectious or toxic substances.

Therefore, before costing an improved drinking-water supply technology, the quality of the water at the source must be assessed and, if necessary, appropriate water treatment must be designed.