Introduction

A water supply scheme collects water from a source, treats it where needed, and delivers it to consumers in adequate quantity and pressure. Rural schemes in Nepal are mostly gravity-based and simple; urban schemes need intake, pumping, treatment and a pipe network.

Rural (gravity) scheme

 Spring/Stream     Intake/Spring box
   (source) ---> [Sedimentation tank]
                        |  transmission main
                        v
                 [Storage/Reservoir tank]
                        |
                   [Break pressure tank] (if head high)
                        |  distribution main
                        v
        [Public standposts / tap stands]

Urban scheme

 [Source: river/lake/well]
          |
      [Intake]
          |  raw water main
   [Raw water pumping station]
          |
  [Treatment plant: screen, sedimentation,
   coagulation, filtration, disinfection]
          |
   [Clear water reservoir]
          |
   [Pumping station]  -->  [Elevated service reservoir]
                                   |
                       [Distribution system]
                                   |
                        House connections

Function of components

In rural areas treatment is limited to sedimentation, sometimes slow sand filtration and chlorination. In urban areas full conventional treatment is provided, and pumping is used where the source is lower than the town.

A gravity water supply system uses the natural fall of ground from a high-level source to carry water to the village without pumping. It is the most common, cheapest and most reliable scheme in the hills of Nepal.

Schematic diagram

  Spring (high level)
       |
  [Spring box / Intake]
       |  pipe (GI/HDPE)
  [Sedimentation tank]
       |
  [Valve + Reservoir tank] <- chlorination
       |
  [Break pressure tank] (if head > 60 m)
       |
  Distribution pipes with air/wash valves
       |
  [Tap stands / Public standposts]

Function of components

1. Source (spring/stream): gives the required yield throughout the year, usually at a higher level than the village.
2. Intake / spring box: collects spring water, protects it from pollution, has an overflow and a washout, and controls the flow into the pipe.
3. Transmission pipeline: carries water by gravity to the tank. Pipes are laid below ground where possible.
4. Sedimentation tank: settles silt and sand, especially for stream sources, before the water enters the tank.
5. Reservoir (storage) tank: stores water to meet the difference between continuous inflow and variable demand, commonly 33 to 50 percent of daily demand. Disinfection (chlorination) is usually done here.
6. Break pressure tank (BPT): reduces the static head to atmospheric pressure so that pipes and fittings are not overstressed.
7. Valves (air, wash-out, sluice, reflux): release trapped air at high points, drain sediments at low points, control flow and prevent back flow.
8. Distribution pipes: carry water from the tank to the settlements.
9. Tap stands / public standposts: the points where users collect water, with a soak pit for waste water.

A water supply system is the set of structures that collects, treats, transmits, stores and distributes water to consumers. A typical urban system is as follows.

Schematic diagram

 [Source: river/lake/well]
          |
      [Intake]
          |  raw water main
   [Raw water pumping station]
          |
  [Treatment plant: screen, sedimentation,
   coagulation, filtration, disinfection]
          |
   [Clear water reservoir]
          |
   [Pumping station]  -->  [Elevated service reservoir]
                                   |
                       [Distribution system]
                                   |
                        House connections

Components and functions

• Source: surface water (river, lake, reservoir) or ground water (well, spring).
• Intake works: draw the required quantity of raw water from the source at a good-quality level and keep out floating matter.
• Raw water pumping and transmission main: lift and carry raw water to the treatment plant where gravity is not enough.
• Treatment plant: screening, plain sedimentation, coagulation and flocculation, filtration and disinfection make the water safe and clear.
• Clear water reservoir: stores treated water, works as a buffer between plant output and pumping.
• Treated water pumping station and main: lift water to the service reservoir or direct into the network.
• Service (distribution) reservoir: stores water at a suitable elevation, meets peak demand, fire demand and emergencies, and keeps uniform pressure.
• Distribution system: the network of main, sub-main and branch pipes with valves, hydrants and fittings.
• Service connections: house connections, public taps and hydrants that deliver water to users.

Objectives of a water supply system (rural Nepal)

1. To supply safe, wholesome water in sufficient quantity for drinking, cooking, bathing and sanitation.
2. To reduce water-borne and water-washed diseases and improve public health.
3. To save the time and effort of women and children who walk long distances to fetch water, and so improve school attendance and income opportunities.
4. To provide water at reasonable pressure and at convenient distance (tap within about 100 to 150 m of each house).
5. To make water available for livestock, small kitchen gardens, schools, health posts and other public uses.
6. To supply water at the lowest cost and to keep the scheme sustainable through user participation and local operation and maintenance.
7. To provide water for fire fighting where needed and to support economic and social development of the community.

Schematic diagram of a rural scheme

 Spring/Stream     Intake/Spring box
   (source) ---> [Sedimentation tank]
                        |  transmission main
                        v
                 [Storage/Reservoir tank]
                        |
                   [Break pressure tank] (if head high)
                        |  distribution main
                        v
        [Public standposts / tap stands]

Components

• Source and intake: spring box or stream intake that collects and protects water.
• Sedimentation tank: removes silt and sand.
• Transmission pipe: carries water by gravity.
• Reservoir tank: stores water and allows for demand variation, usually with chlorination.
• Break pressure tank: removes excess head in steep ground.
• Distribution pipes and valves: deliver water to the settlement and control flow.
• Public standposts / tap stands: point of use for the community.

Necessity of a water supply scheme

Water is needed for life, but natural sources are often far, polluted or seasonal. An organised scheme is necessary because:

• It provides safe water, and so prevents diseases such as cholera, typhoid, dysentery and hepatitis.
• Quantity is assured for drinking, cooking, hygiene and sanitation, which are needed for good health.
• It saves time and labour of fetching water, mainly for women and children.
• It supports schools, hospitals, industries, agriculture, livestock and fire fighting.
• It raises living standards and supports economic growth and planned settlement.

Impacts of water supply schemes

Positive impacts

• Reduced incidence of water-related diseases and lower child mortality.
• Time saved for education, income and rest; better women's participation.
• Improved sanitation and hygiene; growth of toilets, kitchen gardens and small industries.
• Higher land value and better quality of life; employment during construction and operation.

Negative impacts

• Reduced downstream flow, and conflict over water rights when the source is shared.
• Waste water and sludge, causing pollution and mosquito breeding if not drained properly.
• Lowering of ground water table due to over-extraction.
• Land acquisition, loss of forest or farmland during construction, and soil erosion on pipeline routes.
• High capital and maintenance cost, and tariff burden on poor households.
• Over-use and wastage when water is easily available.

Proper planning, environmental assessment and user participation keep the negative effects small.

Objectives of a water supply scheme

1. To supply safe and wholesome water to all consumers.
2. To supply adequate quantity of water for domestic, public, commercial, industrial and fire-fighting needs.
3. To supply water at all times, with sufficient pressure at the tap.
4. To protect public health by preventing water-borne diseases.
5. To make water available at an affordable cost and at convenient distances.
6. To promote economic development and better standards of living.

Requirements of wholesome water

Wholesome water is safe to drink and pleasant in appearance, taste and odour. It should:

• Be free from disease-causing organisms (bacteria, viruses, protozoa, worms).
• Be colourless, clear (low turbidity), odourless and tasteful.
• Be free from toxic substances such as arsenic, lead, cadmium, fluoride and nitrate above limits.
• Contain minerals in permissible amounts (hardness, iron, manganese, chloride, sulphate, TDS).
• Have a pH near neutral (6.5 to 8.5).
• Be free from excess dissolved gases and organic matter.
• Not be corrosive, and not cause scaling in pipes.
• Be palatable and cool, and be available in adequate amount.
• Meet the national standards (Nepal Drinking Water Quality Standards 2062) or WHO guideline values.

Wholesome water is water that is safe to drink and suitable for domestic use. It is free from harmful organisms and chemicals, is clear, colourless, odourless, pleasant to taste, and does not harm health.

Requirements

Physical characteristics

• Turbidity low (Nepal standard: 5 NTU, up to 10 NTU in small supplies).
• Colourless (colour less than 5 TCU, maximum 15) and odourless.
• Pleasant taste; temperature cool (about 10 to 25 degrees C).

Biological (bacteriological) characteristics

• Free from pathogenic bacteria, viruses, protozoa and helminths.
• Zero E. coli / thermotolerant coliform per 100 ml at the consumer's tap.
• Free from algae and other organisms that cause taste, odour or toxins.

Chemical characteristics

• pH in range 6.5 to 8.5.
• Total dissolved solids not above 1000 mg/l; hardness not above 500 mg/l as CaCO3.
• Iron up to 0.3 mg/l, manganese up to 0.2 mg/l, chloride up to 250 mg/l, sulphate up to 250 mg/l.
• Toxic substances within limits: arsenic 0.05 mg/l, fluoride 0.5 to 1.5 mg/l, nitrate 50 mg/l, lead 0.01 mg/l.
• Free residual chlorine about 0.1 to 0.2 mg/l at the tap.

(Values are as in the Nepal Drinking Water Quality Standards, 2062.)

Importance of water

• For life: about 70 percent of the human body is water. It carries nutrients, removes wastes, regulates body temperature and supports digestion and blood circulation.
• For health and hygiene: drinking, cooking, bathing, washing and sanitation depend on water.
• For agriculture and livestock: irrigation and animal needs.
• For industry and energy: processing, cooling, and hydropower generation.
• For community safety: fire fighting, street cleaning and public use.
• For the environment: supports ecosystems, rivers and biodiversity.

Objectives of water supply schemes

1. Supply safe, wholesome water.
2. Supply enough quantity for all uses.
3. Supply at adequate pressure and at all times.
4. Supply at low cost and with easy access.
5. Provide water for fire fighting and public uses.

Necessity of water supply schemes

• Natural sources are often distant, polluted or seasonal.
• Controls water-borne diseases such as cholera, typhoid and dysentery.
• Saves time and labour of fetching water.
• Needed for growth of towns, industries, schools and hospitals.
• Raises the standard of living and supports economic development.

A water supply system is the complete set of works (source, intake, treatment, transmission, storage and distribution) that collects water from a source and delivers it to consumers in adequate quantity, quality and pressure.

Historical development

• Ancient period: Early settlements grew along rivers, lakes and springs. People used hand-dug wells and carried water in pots. The Indus Valley civilisation (Mohenjo-daro, about 2500 BC) had wells and covered drains.
• Roman period: Aqueducts brought water over long distances by gravity to cities; lead and masonry pipes, public baths and fountains were used (about 300 BC to 200 AD).
• Middle Ages: Water supply and sanitation declined in Europe; outbreaks of disease were common.
• 17th to 18th century: Cast iron pipes and steam pumps came in. London and Paris built piped supplies; slow sand filtration was introduced (Paisley, Scotland, 1804; London, 1829).
• 19th century: John Snow showed in 1854 that cholera spreads through water. Pasteur and Koch gave the germ theory. Rapid filtration and chlorination began in the late 1800s and early 1900s.
• 20th century: Chemical coagulation, mechanical filters, ozone and UV treatment, and national standards (WHO) developed.
• Nepal: Ancient stone spouts (hiti or dhunge dhara) in Kathmandu valley supplied water. Piped supply started in 1891 AD (Bir Shumsher), with the Bir Dhara, and later Kathmandu Upatyaka Khanepani Limited and Nepal Water Supply Corporation were formed. Rural schemes expanded under the Department of Water Supply and Sewerage and the International Water Decade (1981 to 1990).

Pollution is a wider term; contamination is mostly related to health hazard.

Requirements of wholesome water

• Free from pathogens and toxic substances.
• Clear, colourless, odourless and pleasant in taste.
• Contains minerals within permitted limits (hardness, iron, chloride, TDS, etc.).
• pH about 6.5 to 8.5.
• Not corrosive and not scale forming.
• Available in adequate quantity and at suitable temperature.

(a) Pure and impure water

(b) Potable and wholesome water

(c) Polluted and contaminated water

Potable water

Potable water is water that is safe to drink; it does not contain harmful organisms or chemicals in amounts that cause illness, although it may have slight taste, colour or odour problems.

Wholesome water

Wholesome water is potable water that is also pleasant to the senses (clear, colourless, odourless, palatable) and has minerals within the desirable limits, so it is suitable for all domestic uses.

Function of water in the human body

• Makes up about 60 to 70 percent of body weight; blood is about 90 percent water.
• Dissolves and carries nutrients and oxygen to cells.
• Helps digestion and absorption of food.
• Removes waste (urine, sweat) from the body.
• Regulates body temperature through sweating.
• Lubricates joints and protects organs and tissues.
• Keeps skin healthy and supports all chemical reactions in cells.

An adult needs about 2 to 3 litres of drinking water daily; loss of 10 percent of body water is serious and a loss of 20 percent can be fatal.

Polluted water

Polluted water is water whose quality has been degraded by the addition of unwanted matter such as sewage, industrial effluent, oil, detergents or agricultural run-off, so that it becomes unfit for its intended use. It may or may not be harmful to health.

Contaminated water

Contaminated water is water that contains harmful micro-organisms (bacteria, viruses, protozoa), toxic chemicals or radioactive substances in amounts that can cause disease. Contamination is always a health hazard.

Function of water in the human body

• Forms about 60 to 70 percent of body weight.
• Carries nutrients, oxygen and hormones through blood.
• Helps digestion and absorption of food.
• Removes wastes through urine and sweat.
• Regulates body temperature.
• Lubricates joints, eyes and mucous membranes.
• Provides the medium for all chemical reactions in cells.

A person needs roughly 2 to 3 litres of drinking water per day.