Water supplies

Water Freedom System

Survive Global Water Shortages

Get Instant Access

Contaminated water can be the vehicle of transmission of a number of disease-producing organisms. Wateris also important in diseases of poor hygiene as a medium for intermediate hosts and as a breeding place for vectors of disease.

The infections and possible improvements that may occur as a result of installing a water supply are shown in Table 3.5.

The provision of water There are four aspects of water supply, which can help to control disease transmission:

• improve water quantity;

• improve water quality;

• reduce water contact by bringing water to site of use;

• prevent spillage by proper maintenance of supplies and drainage.

It will be noticed how this is the normal process in the supply of water. The first objective is to provide water in sufficient quantity, which is followed by improving its quality and finally a piped system is constructed. If this is the pattern followed, then similarly it can be anticipated that the first group of diseases to be reduced will be the water-washed and faecal-oral, then the water-borne etc. However, water supplies need to be maintained and when they break down, the disease can be expected to return.

In rural water supplies where chlorine treatment of the water is costly, difficult to maintain or inappropriate, then a different standard to that in large centralized supplies may be acceptable. This should not be considered unsatisfactory as the provision of a properly constructed water supply is an improvement on what was used before. Also quality is closely related to quantity. By providing a greater volume of water at a more accessible site, quality will usually be improved.

Health aspects are the concern of the medical worker, whereas the villager looks upon water as a basic necessity. His, or rather her (as women are nearly always the carriers of water), major concerns will be quite different. These are the following:

• availability of water at a more convenient place (preferably in the village);

• a continuous and reliable supply;

• additional water for crops and domestic animals.

Table 3.4. Reduction of infection by food protection.

Category Infection Type of food Possible reduction

Table 3.4. Reduction of infection by food protection.

2

Enteric viruses (including hepatitis A and polio)

All

+

2

Hymenolepis

All

+

2

Amoebiasis

All

+

2

Trichuris

All

+

2

Giardia

All

+

2

Shigella

All, especially dairy produce

++

2

Typhoid

All, especially dairy produce

++

2

Salmonellae

All, especially dairy produce

++

2

Campylobacter

All, especially dairy produce

++

2

Non-specific diarrhoeal diseases

All, plus fly contamination

++

2

Cholera

Marine animals, salad

++

2

Leptospirosis

Rat-contaminated foods

++

2

Brucellosis

Milk produce

++

3a

Ascaris

All

+

3b

Taenia

Cow or pig meat

+ + +

4b

Trichinella

Pig

+ + +

4c

Fasciolopsis

Salad

+ + +

4c

Opisthorchis

Fish (fresh water)

+ + +

4c

Paragonimus

Crustacea (fresh water)

+ + +

4c

Diphyllobothrium

Fish (fresh water)

+ + +

Refer to footnote of Table 3.2 for the description of +++, ++ and +.

Refer to footnote of Table 3.2 for the description of +++, ++ and +.

Table 3.5. Expected improvements when installing a water supply.

Category Infection Water improvement required Possible reduction (%)

Table 3.5. Expected improvements when installing a water supply.

Category Infection Water improvement required Possible reduction (%)

Skin sepsis and ulcers

Increase water quantity

50

Conjunctivitis

Increase water quantity

70

Trachoma

Increase water quantity

60

Scabies

Increase water quantity

80

Yaws

Increase water quantity

70

Leprosy

Increase water quantity

50

Tinea

Increase water quantity

50

Louse-borne fevers

Increase water quantity

40

Flea-borne diseases (including

Increase water quantity

40

plague)

2

Enteric viruses (including

Increase water quantity

10?

hepatitis A and polio)

2

Enterobius

Increase water quantity

20

2

Hymenolepis

Increase water quantity

20

2

Amoebiasis

Increase water quantity

50

2

Trichuris

Increase water quantity

20

2

Giardia

Increase water quantity

30

2

Shigella

Improve water quality

50

2

Typhoid

Improve water quality

80

2

Other Salmonellae

Improve water quality

50

2

Campylobacter

Improve water quality

50

2

Non-specific diarrhoeal diseases

Improve water quality

50

2

Cholera

Improve water quality

90

2

Leptospirosis

Improve water quality

80

3a

Ascaris

Increase water quantity

40

3a

Hydatid

Increase water quantity

40

3a

Toxocara

Increase water quantity

40

3a

Toxoplasmosis

Increase water quantity

40

4a

Guinea worm

Reduce water contact

100

4b

Schistosomiasis

Reduce water contact

60

5a

Malaria

Water piped to site of use and

10

5a

Filariasis

maintenance of water

10

5a

Arboviruses

supplies

10?

5b

Onchocerciasis

Water piped to site of use

20?

5b

Gambian trypanosomiasis

80

From Bradley, D.J. (1978) In: Feachem, R.G. etal. (eds) Water, Wastes and Health in Hot Climates. Reproduced by permission of John Wiley & Sons. Ltd, Chichester.

From Bradley, D.J. (1978) In: Feachem, R.G. etal. (eds) Water, Wastes and Health in Hot Climates. Reproduced by permission of John Wiley & Sons. Ltd, Chichester.

It is a combination of these health and social factors that needs to be used in deciding the appropriateness and benefits of water supplies.

Economic and planning criteria Everybody wants the best possible water supply they can get, but resources are limited so it will be many years before everyone has the supply they desire. Decisions have to be made as to which sections of the com munity should be served, when they should receive their supply and the level of availability. There are many alternative strategies that may be, or inadvertently will be, used. They might include the following:

• priority of an area on health grounds;

• priority to an area of water scarcity;

• encouragement of development to an area of high potential;

• priority to communities that can contribute in money and labour;

• political favouritism.

Other alternatives in the nature of the supply can also be considered:

• supplying a large number of people with the simplest of supplies;

• restricting supplies to certain demonstration areas with a high standard;

• start with the most available natural water sources;

• plan a major project, such as a dam, followed by extension of supply in subsequent years.

This will depend on how much the country, region, district or village is prepared to pay for the price of water. Savings can be made by the following: (i) economies of scale; (ii) standardizing the equipment; and (iii) self-help labour.

The initial water master plan is best formulated by skilled engineers, but its execution can be by a purpose-trained technician, utilizing community effort. The plan needs to take account of health, engineering, political and community demands.

Water capacity and use In selecting a suitable source, the amount of water it produces and its regularity need to be known. If a spring or stream does not flow all the year round, then it is not suitable unless a dam is also built. Measurements of water flow should be made at the end of the dry season and the people asked if the source has ever dried up. A temporary dam can be constructed and the rate of filling a measured bucket estimates the flow. Wells can be mechanically pumped out and the fall noted for a given flow of water. Rainwater catchment is derived from the simple formula:

1 mm of rainfall on 1 m2 of the roof in plan will give 0.81 of water.

As an example, if the roof plan area is 10 m x 5 m and the average annual rainfall is 650 mm, then 10 x 5 x 650 x 0.8 = 26,000 l/year or 71 l/day, on average.

The demand for water will be determined by the availability, the number of people and the use to which it is put. Availability is the most crucial factor as water that has to be carried some distance will be used much more sparingly than when there is a tap inside the house. Average figures taken from a number of studies are as follows:

Rural supply Standpipe

Single tap in the home Multiple taps with bath, W.C., etc.

20 l/person/day 40 l/person/day 80 l/person/day

200-300 l/person/day

At least 50% extra capacity is allowed for future growth of the community and expansion of the supply. A water source is chosen where the expected demand on the supply will never be exceeded, even in the driest time of the year. If this is not possible, then some form of storage will be required. Water use during the night is far less than during the day, so a poor supply can be boosted by providing a storage tank that fills at night. In areas of wide seasonal variation, more extensive storage facilities may be required, such as a dam, to save the rainfall in the few wet months.

Choice of water supply Choosing a water source will depend upon the following:

• technical feasibility;

• resources available;

• social desirability or taboo;

The alternative choices are illustrated in Figs 3.5 and 3.6. Rainwater naturally seeps through the earth until it finds an impervious layer (such as clay) on which it collects. When this impervious layer comes to the w

Fig. 3.5. Sources of water.

Fig. 3.6. Water catchment and the fresh water lens of coral islands.

surface, water runs out of the ground as a spring. It can also form the bed of a river or in an enclosed area, a lake. This groundwater can be tapped by a shallow well. At a much deeper level, a second impervious layer can trap a large quantity of water. A deep well or bore hole is required to reach this source of water. Island populations (Fig. 3.6) have particular problems in obtaining water and are generally left with only two alternatives. Provided they have suitable roofing material (e.g. corrugated iron), rainwater can be collected and stored in a tank. The other alternative is to sink a well to tap the freshwater lens. Due to a fortunate quality of coral rock, it acts like a large sponge, holding fresh water that has percolated through, floating on the denser sea water. Provided the well is sunk just far enough and not pumped out too hard, freshwater can be obtained. The different water sources are summarized in Table 3.6.

Wells are often a good supply, as long as contamination can be prevented and have the advantage that they can be sited close to houses. This can be achieved by sealing them and having a pump fitted, but this will require maintenance. Deep wells and bore holes need special equipment for their construction and complex pumps to lift water from these depths. They are mainly applicable in areas of severe water shortage such as deserts. Lakes and rivers provide conveni ent, but poor quality water. Other sources should be used if possible, but if there is no alternative, then some form of water treatment, such as filtration and storage, should be incorporated. A constant spring that never dries up is a very suitable source, as it is comparatively free from contamination and can normally be led to an outlet without requiring pumping. Maintenance costs will, therefore, be low, so greater capital expenditure can be allowed for protecting the spring and piping its water to the village.

Rainwater catchment is an underutilized source of pure water, either as a main method or as subsidiary (for drinking water). So much good water runs to waste off large expanses of roof that have already been paid for in the construction of the building. This water can be tapped for good use. With the additional cost of guttering and a tank, a family can have a good, safe source of water inside or very close to their house. Storage tanks can either be close to the roof or large concrete structures built underground. Their main danger is that if water is allowed to collect in poorly maintained gutters or uncovered tanks, then mosquitoes can breed there.

The ideal is to find a source that has both constant quantity and good quality, but where the latter is not available, then it can be improved by simple methods, such as the three-pot system (Fig. 3.7).

Table 3.6. Sources of water, their advantages and disadvantages.

Spring

Shallow well

Bore hole

River

Lake

Catchment

Proximity

Distant

Near

Intermediate

Near

Near

Near

Reliability

Good

Variable

Good

Unreliable

Good

Unreliable

Quantity

Good

Moderate

Good

Variable

Good

Poor

Quality

Good

Moderate

Good

Poor

Poor

Good

Technology

Easy

Moderate

Difficult

Easya

Easya

Moderate

Cost

Low

Moderate

High

Lowa

Lowa

Moderate to high

Community

High

Moderate

Moderate

Low

Low

Moderate

preference

Maintenance

Low

Moderate

High

Low

Low

Moderate

aThese assessments are for taking water by hand from the river or lake. If a pump and supply system are used, then the technology is difficult and the cost high.

aThese assessments are for taking water by hand from the river or lake. If a pump and supply system are used, then the technology is difficult and the cost high.

Only the top clear water that has been standing all night is poured off for drinking

Fig. 3.7. The three-pot system - a simple means of improving water quality.

Was this article helpful?

0 0
Allergy Relief

Allergy Relief

Have you ever wondered how to fight allergies? Here are some useful information on allergies and how to relief its effects. This is the most comprehensive report on allergy relief you will ever read.

Get My Free Ebook


Post a comment