CHAPTER 1
Improved water supplies
In contrast with the wealthier (and wetter) parts of the world, where it is estimated that people use 150 litres of water per person each day, in dry regions an individual must often manage with only 5 litres per day – less than a bucketful – for drinking, cooking, personal hygiene and cleaning of all sorts. To put this into context, an automatic washing machine uses at least 40 litres per cycle, and modern flush-toilets use a minimum of 3 litres with each flush. Women and children often walk miles to collect these small but nonetheless heavy amounts of water for their families, using time and energy that could otherwise be used for education, small enterprise, or recreation.
If the water is contaminated because animals also use it, or because of seepage from badly sited latrines, ill-health inevitably follows. Those afflicted by poverty or ill-health may not have the energy to remedy their situation – and yet remedies are often within their means, if the appropriate information and skills can be made available. The technologies described here are just a few examples of innovations that can make a difference to the cost, in financial or human terms, of essential supplies of water.
Some rain falls almost everywhere that people live, and this can be collected for household use by installing suitable pipes and tanks, as shown in the example from Kenya. In South Africa, a children's merry-go-round has been produced that pumps water from boreholes faster than the average hand-pump, and in Somalia, where irrigation schemes have operated successfully in the past, water user associations have been mobilized to harness local skills for cleaning and rebuilding the old canals and learning to maintain new and specially adapted pumps. Again on the larger scale, specially designed bags can be used to transport clean water by sea and river to communities who are reliant on imported water, as on some Greek islands.
In mountainous areas like Nepal, water may be plentiful but inaccessible, and here the hydraulic ram can provide a low-cost answer. Where water is available but contaminated, as in Bangladesh, everyday items such as saris can be used to filter out the bacteria. All these ideas can be adopted and adapted as appropriate to enable a community to fulfil its requirement for water.
Saris as water filters
Bangladesh, unlike many developing countries, has an abundance of water, but it is frequently contaminated by bacteria which cause life-threatening diseases such as cholera. Cholera is a major cause of illness in many developing countries and Bangladesh is no exception. In 1998, there were about 1000 people entering the hospital in Dhaka every day who were affected by the disease.
The poor are most at risk from water-borne infections as they tend to be undernourished, lacking in proper sanitation facilities, and with little access to medicine. Children and the elderly are especially vulnerable because their immune systems are either undeveloped or worn out. For developing countries, there may be a problem with finding the money to pay for treatment and to make the changes in infrastructure that will prevent the disease becoming an epidemic or endemic (always present).
Cholera
The bacteria that cause cholera are known as Vibrio cholerae and are consumed by drinking contaminated water or by eating food that has been contaminated. Once they pass the stomach and enter the small intestine, they start multiplying and release a toxin which causes severe diarrhoea and vomiting. As a result the sufferer becomes severely dehydrated, which causes death unless the fluids being lost are quickly replaced.
The bacteria are normally found associated with free-swimming, microscopic animals called copepods. Each copepod carries thousands of cholera bacteria and so if even a small number of these creatures are ingested through drinking contaminated water, or by eating fresh fruits or salads, there is a strong risk of infection. Plankton blooms occur in spring and autumn in Bangladesh, and each bloom is invariably followed by an outbreak of cholera.
There is no vaccine effective for cholera, and it can never be eradicated because the bacterium is part of the natural environment. All human faeces contain large numbers of bacteria and, without good sanitation systems, excreta and pathogens enter water from faeces. This is a particular problem where people are suffering from watery diarrhoea, such as occurs with cholera. One person with cholera excretes enough bacteria each day to infect up to 10 million people (Jones 1994).
People drinking safe water are still at risk of contracting cholera if they continue to use pond or river water contaminated with cholera bacteria for bathing, cooking, and washing fruits, vegetables and utensils. It is therefore essential to separate the disposal of excreta from water used for drinking. This is usually carried out on a small scale by building latrines or septic tanks where excreta can be held and prevented from seeping into nearby watercourses. However, in the absence of funds for this kind of development, alternative means must be found to reduce the incidence of cholera.
Decontaminating drinking water
Water can be sterilized by boiling but this is an uneconomical method because wood for fuel is extremely scarce in Bangladesh, as in many other developing countries. Tests of water samples have shown that filtering out the copepods would also remove the bacteria and so, rather than using expensive methods of killing the copepods and bacteria, it is practical to remove them from water for household use.
The sari as a filtration tool
A sari is a rectangular piece of cloth measuring 5–6 metres in length. The style, colour and texture of the cloth vary and it can be made from cotton, silk or synthetic materials. For centuries, the sari has been worn by millions of women throughout the world and, in Bangladesh, people sometimes use the sari to remove particles and insects from sugar or molasses, which are commonly used to make a local drink. The sari is now being used to filter drinking water in an attempt to reduce the occurrence of cholera.
To filter the water effectively, the sari needs to be folded so that there are four to eight layers of cloth. The folded cloth is then wrapped over the water pot before water is collected from the pond or river. Once the water is in the pot, the sari is removed, unfolded and rinsed in the pond or river, or in a small amount of the filtered water. It must then be dried in the sun for a couple of hours, a process of natural decontamination. This is sufficient to kill off any bacteria trapped in the material but, if drying is not possible because of insufficient sunlight, as in the monsoon seasons, cheap disinfectant can be used to decontaminate the material. It is essential that the cloth is unfolded and cleaned each time it is used.
Sari material is excellent for filtration purposes as it is thin and easy to dry and, as saris are found in every household in Bangladesh, this method is affordable even to the poorest of the poor. Laboratory tests have shown that filtering water through four layers of sari material can remove 99 per cent of the bacteria attached to the copepods and particles, and thereby reduce the infectious dose of cholera present in water. This is because the tiny bacteria are attached to the much larger plankton and particles, so they can be filtered out easily. The chances of consuming a large enough dose to cause cholera are thereby dramatically reduced. Any more than four layers of cloth can lead to the clogging of the filter and so increases the filtration time significantly.
The technique of filtering bacteria out of water could be successfully adopted in other parts of the world, using almost any material that is thin and dries easily.
Further information
Research Associate Professor
University of Maryland Biotechnology Institute
Columbus Centre
701 East Pratt Street
Baltimore
Maryland 21202
USA
Tel: +1 410 234 8833/8886
Fax: +1 410 234 8873/8896
E-mail: huq@umbi.umd.edu
Rainwater catchment systems
Two-thirds of Kenya is arid or semi-arid and so access to water is difficult. Half the population has no access to a safe or adequate supply of water and must share a distant water source with animals that drink from it and contaminate it.
The annual rainfall in Kenya ranges from 150 mm to 2000 mm and rainwater is the most commonly accessible source of water. Rainwater catchment systems have a long history, but until recently this simple yet effective method of water collection and supply has been regarded as a last resort. The Kenya Rainwater Association decided to help develop rainwater harvesting technologies in the rural areas.
Uses of domestic water
In times of drought or other crises it is not uncommon for the per capita water consumption to fall below the accepted minimum of 5 litres per day, which covers the following essential purposes:
• drinking
• food preparation and cooking
• personal hygiene
• washing clothes and cleaning
• washing pots, pans and other utensils.
Additional domestic water requirements may include:
• watering gardens
• water for animals
• water for construction (e.g. repairing mud walls).
In most areas, properly designed household roof catchment systems can normally meet domestic demand for essential purposes.
Rainwater catchment systems
Every rainwater catchment system consists of three main components:
• a catchment surface where the rainwater is collected
• a storage reservoir where the rainwater is stored until required
• a delivery system for transporting the water from the catchment system to the storage reservoir, consisting of gutters and drains.
The actual amount of rainwater that can be supplied depends upon the amount and distribution of rainfall, the size of existing or affordable catchment surfaces, and the volume of the storage tank.
Roofs provide the most common and least expensive way of collecting or harvesting rainfall. Corrugated iron, plastic or tiles all make good surfaces for rainwater catchment, but tightly thatched roofs made from coconut palms may be equally suitable.
Storage tank design
For most rainwater harvesting systems, the storage tank represents the greatest single cost. This is especially true for roof catchment systems where an existing roof structure provides, in effect, a free catchment area.
The key features of any tank are that it should be watertight, durable, affordable and not contaminate the water in any way. The most appropriate choice of tank will depend on local conditions and the materials that are available locally, as this will directly affect the cost. Bricks, blocks, concrete or ferro-cement can all be used to build the tank walls.
There are a number of key requirements common to all effective tank designs:
• a functional and watertight design
• a solid, secure cover to keep out insects, dirt and sunshine
• a screened inlet filter
• a screened overflow pipe
• a manhole (and ideally a ladder) to allow access for cleaning
• an extraction system that does not contaminate the water, e.g. tap or pump
• a soakaway to prevent spilt water forming puddles near the tank
• a maximum height of 2 metres to prevent high water pressures (unless additional reinforcement is used in the walls and foundations).
Construction of the water storage tank
The site needs to be free of anthills, latrines, waste pits and tree stumps to ensure that a solid foundation can be built for the tank. Once a suitable site has been found, a circle is drawn on the ground with a radius 15 cm longer than the external radius of the tank. The foundation must be sealed with concrete within 24 hours or there is a danger of leaks and cracks. The tank walls should be round as these are stronger than rectangular walls. It is essential to cover the tank with a roof to prevent evaporation and stop the water becoming dirty.
The delivery systems usually consist of gutters suspended from the eaves sloping towards a downpipe and tank. The gutters must be fitted properly to ensure that they operate at optimum capacity. They should be angled with a gentle slope leading into the tank.
Group cooperation
As a result of the work carried out by the Kenya Rainwater Association, rainwater catchment systems have been adopted by women's groups in the Laikipia district in Kenya. Money is collected by the women and as soon as they can afford to buy the materials to build a water tank, they pick a member by drawing lots and then start to build a rainwater tank in her compound. They hire a skilled worker to guide them but carry out most of the building work themselves.
The women, who used to walk about 10 km with water on their backs, no longer have to spend hours collecting water and can spend more time on growing vegetables or poultry farming, thereby improving the family diet. Some women have even started to plant trees and sell seedlings to generate extra income and they can now afford to send their children to school.
Hydraulic ram pumps
For the people living in the upland Himalayas, access to water is limited and women spend hours walking to collect enough water for their daily needs. In Nepal, in the village of Galang, the introduction of a hydraulic ram pump more than a decade ago has changed the lives of the local community by bringing water to the villagers and freeing up their time for other activities.
The automatic hydraulic ram is a pumping device for lifting water to heights of over 100 metres. It has been widely used for more than two centuries in many parts of the world. The pump works by using the energy of a large amount of water falling a small height to lift a small amount of that water to a much greater height. In this way, water from a spring or stream in a valley can be pumped to a village or irrigation scheme on the hillside. Wherever a fall of water can be obtained, the ram pump can be used as a relatively cheap, simple and reliable means of raising water to considerable heights.
It is an ideal machine for water pumping if certain conditions are satisfied, because it works solely on the power from falling water carried in a pipe from a spring, stream or river without any need for an additional power source. However, it cannot be used everywhere. For example, it cannot be used to pump still water from a well, pond or lake unless there is a separate, flowing water source nearby. These conditions restrict the use to three main applications:
• lifting drinking water from springs in valleys to settlements on higher ground
• pumping drinking water from clean streams that have a significant slope
• lifting irrigation water from streams or raised irrigation channels.
In Galang, the ram pump provides one hundred families with water for their daily requirements. Each villager pays a small monthly fee to the manager and maintainer of the ram pump to ensure that the pump and pipes are kept in good working order. For any similar scheme to be successful, it is essential for someone to take on the responsibility for calling meetings to discuss management and any particular problems, and to carry out the maintenance work.
Ram pump operation
Although ram pumps come in a variety of shapes and sizes, they all have the same basic components. The flow of water at the source needs to be measured to establish whether it is enough to operate the ram. Naturally occurring sources of water tend to dry up during the year and this needs to be considered.
Ram pumps have a cyclic pumping action that produces their characteristic beat during operation. The cycle can be divided into three phases: acceleration, delivery and recoil.
Acceleration
Normally, the impulse valve remains open due to gravity so, when the supply is connected, water accelerates down the drive pipe and starts to escape past the open valve. As the water passes around the valve, it tends to drag it closed and, when this drag reaches a critical level, the valve starts closing. Once the valve has begun to move, it closes very quickly.
Delivery
As the impulse valve slams shut, the escape of water is stopped. However, the water already flowing in the pipe has considerable momentum which must be dissipated. For a fraction of a second, the water in the body of the pump is subjected to a large and sudden surge in pressure. This pressure rise, known as 'water hammer', forces water to surge through the delivery valve which is held open by the flowing water. The surge takes the water up the delivery pipe and high into the air vessel until the pressure in the main pump body falls off. The water in the delivery pipe then tries to flow back, closing the delivery valve.
Recoil
The remaining flow in the pipe recoils against the closed delivery valve – rather like a ball bouncing back. This causes the pressure in the body of the pump to become low enough for the impulse valve to reopen. The recoil also sucks a small amount of air in through the snifter valve. The air sits under the delivery valve until the next cycle, when it is pumped with the delivery water into the air vessel. This ensures that the air vessel stays full of air. When the recoil energy is finished, water begins to accelerate down the drive pipe and out through the impulse valve, starting the cycle again.
