Borehole construction is greatly influenced by local factors and relatively unknown underground conditions. Several drilling and construction techniques have been developed for use in these different environments.
Also, the selection of the correct material required is of extreme importance. Boreholes are very suitable for drinking water supply because simple precautions will be adequate to safe-guard the water against contamination. In some cases either vertical or horizontal water collectors, or a combination of the two, can be appropriate.
When groundwater is withdrawn there is always a lowering of the groundwater table. The possible effect of an appreciable lowering of the groundwater table should be carefully investigated. Most of the more convenient source of water for small communities is frequently a natural stream or river close by. A river intake should be sited where there is an adequate flow and the level allows gravity supply to minimize pumping costs.
The quality of the water is also important so the water intake should be upflow of density populated or farming areas or of cattle watering places. Intake design should avoid clogging and when the river transport rolling stones or boulders a protection in concrete, stone or brick of the intake may be necessary.
At the water intake a screen is usually placed, to remove to remove floating or suspended matter of large and small size. The bottom of the intake structure should be at least 1 m above the riverbed.
A submerged weir may have to be constructed downstream of the intake to ensure that the necessary depth of water is available even in dry periods. The quality of lake water is influenced by self-purification through aeration, bio-chemical processes and settling of suspended solids.
In deep lakes, wave and turbulence will not affect the deeper strata. As there is no mixing, a thermal stratification will develop, which can be fairly stable and should be taken into account when choosing the location and depth of a lake water intake for water supply purposes. Deep lakes will have towards the bottom water with a low nutrient content and good chemical quality that will be same throughout the full depth.
Provision should be made to withdraw the water at some depth below the surface. River and lake intakes should be periodically checked and floating material and debris should be periodically removed from the screens and weir. Checks for any damage of intake, bank protection and weir from heavy materials or from heavy flow from debris need to be made.
In many situations treatment of raw water is necessary to make it suitable for drinking and domestic use. In most developing countries small towns and rural communities are not able to run complicated water systems that surmount local capacity and feasible regional support structures. The construction and running costs, and the operational and maintenance needs are key factors that must be considered carefully when planning and designing a small water treatment plant.
Water treatment should be combined with other strategies as watershed and land use management to protect surface and ground water, selection and protection of the best available water sources, adequate and well-maintained distribution system. A good drinking water quality depends on more than water quality enhancement or water treatment processes.
The types of risk existing in the supply source and the institutional and socio-economic conditions prevailing in the target community determines the level of water treatment technology. The best approach is the multi-stage water treatment: successive stages progressively remove contaminants from the raw water and consistently produce safe and wholesome final water. Strengths and weaknesses of each treatment stage should be quantified and balanced, so that all contaminants are effectively removed at a feasible cost.
The final stage of the water treatment will be disinfection. It is effective only if the previous stages have removed most of the waterborne pathogens and reduced solids or other contaminants.
This should allow the use of only a small dose of disinfectant. The main health risk related to water supply systems that use surface water is contamination with waste water.
This introduce a big variety of bacteria, viruses and protozoa and can cause waterborne diseases. All pathogenic organisms as well as high risk chemical substances such as heavy metals , fluoride , arsenic , nitrate and organic constituent must be removed.
Other substances that needs to be removed or considerably reduced are suspended solids causing turbidity, iron and manganese compounds imparting a bitter taste or staining laundry, and excessive carbon dioxide corroding concrete and metal parts. For small community water supplies other quality characteristics such hardness, TDS and organic content would generally be less important. Click here for quality guidelines for drinking water. Some water treatment processes serve a single purpose and others have a multiple applicability.
Often a treatment result can be obtained in different ways. The following table summarize the removal of some water contaminants by various treatment processes. This comparison is obviously general because there are many factors to take into account. A detailed description of water treatment processes for small community water supplies will follow.
Groundwater treatment : Groundwater, if properly withdrawn, will be free from turbidity and pathogenic organisms and if it originates from a clean sand aquifer, other hazardous substances will also be absent. In this case only disinfection is recommended, groundwater can be used without any further treatment. When groundwater comes from an aquifer containing organic matter, the oxygen content may be depleted and the water may be able to dissolve iron, manganese and heavy metals.
Aeration and filtration can remove these substances. Sometimes groundwater contains also fluoride, arsenic and salts or may be polluted by hazardous waste and if no alternative source of water is available, these polluted sources may have to be used.
In this case the source should be treated with chemical coagulation and flocculation, iron exchange and different filtration technologies, including GAC. Unfortunately many of these treatment processes involve expensive technologies, but they are necessary to make the water suitable for drinking and domestic purposes.
Surface water treatment : Water in surface sources originates partly from groundwater outflows and partly from rainwater that has lowed over the ground to the receiving bodies. The groundwater outflow will bring dissolved solids into the surface water, while the surface run-off is the main contributor of turbidity and organic matter, as well as pathogenic organisms.
In surface water bodies the dissolved mineral particles will remain unchanged, but the organic impurities are degraded. Unpolluted surface water of permanently low turbidity may be purified by slow sand filtration, or by direct rapid filtration followed by chlorination. SSF has the advantage of low operational requirements. When the turbidity of the water is high, or when algae are present, SSF units would rapidly clog.
In this case pre-treatment is needed, such as sedimentation, coarse gravel media-filtration, rapid filtration or a combination of more of these processes. Chemical coagulation and flocculation can improve the removal by settling and filtering of colloidal suspended particles.
During water treatment it is important not only to have an assessment of the raw water quality, but also performance efficiencies and treatment objectives for the treatment plant. Aeration is the treatment process whereby water is brought into intimate contact with air. Aeration is widely used for the treatment of groundwater having too high iron and manganese content. Ferrous and manganese compounds will react with the atmospheric oxygen brought into the water through aeration.
They will be transformed into insoluble ferric and manganic oxide hydrates that can be subsequently removed by sedimentation or filtration. It is important to know that when the water contains organic matter, the formation of iron and manganese precipitates through aeration is likely to be not very effective.
In this case it might be necessary to use chemical oxidation, alkalinity variation or special filters. These methods however are expensive and complex, so often they are not suitable for rural communities in developing countries.
The intimate contact between water and air for drinking water treatment is mostly achieved by dispersing the water through the air in thin sheets or fine droplets water fall aerators or by mixing the water by disperse air bubble aerators.
Coagulation and flocculation provide the water treatment process by which finely divided suspended and colloidal matter in the water is made to agglomerate and form flocs.
Colloidal particles are midway in size between dissolved solids and suspended matter and are kept in suspension by a balance between electrostatic repulsion and hydration. Colloids usually have a surface charge due to the presence of a double layer of ions around each particle, and this charge is responsible for electrostatic repulsion. This electrostatic repulsion between these negative charges cancels out the electronic attraction forces that would attach the particles together.
Some chemicals called coagulants are able to reduce the range of electrostatic repulsion, by compressing the double layer of ions around the colloidal particles.
They enable the particles to flocculate, forming flocs that can grow to a sufficient size and specific weight to allow their removal by settling, filtration or flotation. The substances that are frequently removed by coagulation and flocculation are those that cause turbidity and colour.
Generally water treatment processes involving the use of chemicals are not suitable for small community water supplies. Iron salts or ferric sulphate are also used, with the advantage that they can be used in a broader pH range for good coagulation. Sodium aluminate is mostly used for coagulation at medium pH. Synthetic organic polyelectrolytes have become available as coagulants, but they are generally not economical for small water supply systems. For good coagulation the optimal dose of coagulant can be determined with a laboratory experiment called the jar test.
The optimal dose depends upon the nature of the raw water and its overall composition and it is the lowest dose of coagulant that gives satisfactory clarification. In developing countries women from the lower classes have discovered that some seeds contains substances for the growth of the seedling that also have flocculating properties, i.
These seeds coagulants are more sensitive than alum to the mineralogical composition of suspended matter, and are mainly applicable in tropical and subtropical countries at rather high temperatures. Teachers or commercial outlets involvement is required to help to determine the optimal seeds coagulant dose, and to distribute or sell standard solutions of the seeds coagulants.
To rapidly disperse the entire dose of chemicals throughout the mass of the raw water, rapid mixing is used. This is realized using hydraulic or mechanical rapid mixers, which should be located near the building where the solutions or chemical are prepared.
The next stage after rapid mixing is flocculation. Flocculation is the process of gentle and continuous stirring of coagulated water to form flocs through the aggregation of minute particles present in the water. There are mechanical and hydraulic flocculators : in mechanical flocculators the stirring of the water is achieved with devices such as paddles, rakes or paddle reels, in hydraulic flocculator the stirring results by the action small hydraulic structures.
Sedimentation is the settling and removal of suspended particles that take place when the water stands still in, or flow slowly through a basin. Turbulence is generally absent or negligible, and particles having a specific weight density higher than that of the water are allowed to settle. These particle will deposit on the bottom of the tank forming a sludge layer and the water reaching the outlet of the tank generally place on the top on the side opposite to the feed will be in a clarified condition.
Settling tanks need to be regularly cleaned to remove the sludge layer formed on the bottom. The calculation of the settling velocity helps to determine the efficiency of a settling tank. The settling velocity s of a particle that in detention time T will just traverse the full depth H of the tank is:. From the ratio you can see that the settling efficiency basically only depends on the ratio between the influent form rate and the surface area of the tank.
This is called surface loading. Particles having a settling velocity s higher than s 0 will be completely removed, and particles that settle slower than s 0 will be removed for a proportional part s:s 0. Where sedimentation is used without pre-treatment the surface loading generally should be in the range from 0.
Tanks for small water treatment plants are generally rectangular with horizontal flow. Settling tanks with vertical walls are normally built of masonry or concrete; dug settling basins mostly have sloping banks of complicated ground with a protective lining, if necessary. An improvement in settling efficiency can be obtained by the installation on the bottom of trays, plates or tubes. Nevertheless it is important to remember that more sludge will be generated, so additional removal facilities may be required.
In small community water supplies dissolved air flotation DAF can be used particularly for the flotation of algae, which can give rise to the filtration problem if not reduced. DAF consist in the injection in the tank of fine bubbles that make it possible to collect and remove fine light particles, such as flocs containing colour or algae. The basic technology in rather complex and can involve more steps, such as chemical addition and mixing, flocculation, injection of water saturated with air under pressure, nozzles for the pressure release, a filtration tank and rapid filtration.
For this reason it would not normally be advisable to use this process in small community water supply. This combination allows the treatment of water with considerable levels of contamination and it is a robust and reliable treatment method that can be maintained by operators with low levels of formal education.
It is much better suited than chemical water treatment to the conditions in rural communities and small and medium municipalities. Slow sand filtration : The water treatment in SSF is the result of a combination of physio-chemical and biological mechanisms that interact in a complex way. Soluble matter in the sand bed is consumed by bacteria and other micro-organisms.
The main physical mechanisms contributing to particle removal are surface straining, interception, transport, and attachment and detachment mechanism. A SSF unit basically consists of a structure containing flow control and drainage systems, a supernatant water layer and a filter bed.
For continuous supply there should be at least two units operating in parallel. To maintain the proper filtration rate through the filter bed outlet and inlet- controlled flow can be used. In the outlet controlled flow the outlet valve is gradually opened to compensate the increase in the head loss over the filter media. The supernatant water level is always kept close to maximum.
In the inlet-controlled filters an increase in head loss is compensated by an increase in the height of the supernatant water. The layer of supernatant water provides the static head necessary for the passage of water through the sand bed. The sand to be put into the SSF should be clean and free of clay, earth and organic material. The presence of dust seems produce high initial head losses and to limit the essential development of an active and effective microbial population in the filter bed.
SSF units must operate continuously, since this contributes to a better quality effluents and a smaller filtration area required. After several weeks or months of running, the SSF unit will gradually become clogged.
By scraping of the top layer of the filter bed, the hydraulic conductivity will be restored after a secondary ripening period usually days. Scrape sand should be washed and stored. After several filter runs this activity leads to a gradual reduction of the sand bed depth unit a minimum value 0.
Then re-sanding become necessary. Great differences exists in the application of SSF technology, depending on water quality standards, raw water quality, type and level of pre-treatment and local conditions.
Even if high removal efficiencies can be obtained, SSF alone cannot always produce water of high standard. Limitations can be due to the presence of the following contaminants and parameters:.
Suspended solids or turbidity: suspended solids can create major increases in head loss and adverse conditions for the biomass active in the filtering bed. Algae : a massive algal growth can cause a quick reduction of the permeability of the filtering bed. Low temperature: low temperature increases the viscosity of the water and reduces the biological activity in the sand bed. Nutrients : the micro-organisms active in the sand bed require nutrients carbon, nitrogen, phosphorous and sulphur for their metabolism and growth.
The total absence of nutrients in the incoming water can decrease the SSF efficiency. Dissolved Oxygen : with low levels of dissolved oxygen the filter skin can develop anaerobic conditions.
This can create serious water quality problems, such as bad smell and taste. Surface waters presenting relatively moderate to high levels of contamination could not be treated directly by SSF units. During the last few decades pre-treatment alternatives have been developed to extend the application of SSF to poorer water sources without requiring skilled staff, complex mechanical equipment or chemical supplies, i. Coarse media filtration : In coarse media filters porous media such gravel and sand are used as pre-treatment.
In dynamic gravel filters the water enters the unit and passes through the fine gravel to the drainage system. With moderate levels of SS in the source water, this fine gravel would eventually clog. If quick changes occur, the clogging may be much faster. Eventually the gravel bed will be blocked and the total water volume will just flow over the clogged surface are to waste, protecting the subsequent treatment steps that are more difficult to maintain. Depending on the flow direction in the layer of gravel, the second treatment step are upflow, downflow or horizontal flow systems.
Head loss in CMF is small, usually a few centimetres, with a maximum value around 0. Since the CMF units in small water supplies systems deal with low flow and low pressure values, some simplified valves, gates, and weirs can be used together with more commercial hydraulic devices.
The main criteria for CMF design are removal efficiency and head loss related to particle retention in the filtering bed. The filtering media should have a large surface area to enhance particle removal and a high porosity to allow the accumulation of the separated solids. Tests showed that neither the roughness nor the shape of the filter materia had a great influence on filter efficiency. Gravel is the commonly used material, but broken bricks, palm fibre and plastic material can also be used.
Operation on CMF units required a frequent at least daily control of the influent and effluent flow and the quality of filtered and raw water.
Maintenance is associated mainly with the cleaning process. To facilitate it, a minimum of two units should be constructed in parallel. Frequent cleaning of CMF is recommended to limit head loss development and to avoid operational problems. In general, performance findings of MSF are very satisfactory.
Nevertheless, the performance may be different in different regions of the world. Much depends on the characteristics of the raw water turbidity, SS, particle size distribution, temperature, true colour and partly on climatic seasonal fluctuations.
MSF can adapt itself to the type of raw water and the concentration of contamination. MSF technology has a great potential to reduce the physical-chemical and the bacteriological risk associated with surface water sources.
The cost efficiency of MSF systems increases with the size of the system. The operational and maintenance cost is mainly determined by labour cost. Capital and running costs increase with increasing contamination levels in their raw water types. Sand is also the media commonly used in rapid filtration, but much coarser sand than in SSF is used, with an effective grain size in the range 0. This coarse sand allow the impurities to penetrate deep into the filter bed, giving to it an high capacity to store deposited impurities.
Cleaning of rapid filters is effected by backwashing: an high rate flow of clean water is sent back through the filter bed. This backwash water carries away the deposited material that was clogging the filter.
Cleaning of rapid filters is quick and can be done as necessary as required, even everyday. Facebook Twitter LinkedIn Syndicate. Water Sources. Minus Related Pages. On This Page. Environmental Protection Agency. Factoids: drinking water and ground water statistics for March , April Severe drought in Kenya has forced Enow Wanyo and Budha Tura to gather water from a muddy puddle, 30 minutes from their village. People and animals are competing for water that is often contaminated.
Concern is providing aquatabs to sterilize the water. Photo: Jennifer Nolan. As the saying goes, you can have too much of a good thing. Flooding and severe storms can wash away communities and infrastructure in an instant. We saw this happen last year with Cyclone Idai, which devastated communities in Mozambique, Zimbabwe, and Malawi.
As part of our emergency response efforts, we delivered short-cycle crop seeds to the areas of Malawi and Mozambique that were hit hardest. Ernesto Gambulene with the ruined maize crop from his field in Lamego, which was inundated by floodwaters from Cyclone Idai for nearly two weeks.
He is the father of 7 children and the family home was also destroyed. Photo: Kieran McConville. During this recovery period, Concern gave many fishermen training and jobs at boat yards, repairing boats for their fellow fishermen and rebuilding their own fishing businesses with boats provided by Concern. Nolito Dela Cruz and his family lost their home and boat during Typhoon Haiyan.
Slowly they managed to rebuild, they also received a new boat from Concern Worldwide so they can continue their livelihood of fishing. Photo: Steve De Neef. Health, food, gender equality, economic markets, and even education are adversely affected by water scarcity and restricted access to sanitation which, for us, goes hand-in-hand with water. We have dug, drilled, and bored thousands of wells in remote and disadvantaged communities across dozens of countries over the past 50 years and built countless latrines in their schools and health centers.
The hours saved and the illnesses prevented make it one of the most effective things we do. Stencil a message next to the street drain. This reminds people not to dump waste into a street drain, which leads to local water sources such as rivers. You can also use stencils to produce and distribute flyers to your neighbors. Post signs along the border of your source water protection area to notify people that any pollution in that area can affect the quality of local drinking water.
Water is a shared resource. You can work within your community, watershed, or neighborhood to protect your drinking water. Many partners are involved in implementing source water protection through watershed management strategies involving:. States have completed the first step of assessing the protection area for all public water systems. Each assessment includes a delineation, a contaminant inventory, and susceptibility determination.
You may find that the assessment in your local area is outdated. Water utilities provide the public with information, safety monitoring, and emergency response. They have a critical role to play in promoting source water protection, including:.
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