Water Supply PDF

UNIT ONE WATER SUPPLY Table of Contents UNIT 1 - WATER SUPPLY....................................................................................................... 2 OBJECTIVES:.........................................................................................................................

UNIT ONE WATER SUPPLY Table of Contents UNIT 1 - WATER SUPPLY....................................................................................................... 2 OBJECTIVES:............................................................................................................................ 2 SECTION 1: INTRODUCTION................................................................................................. 3 SECTION 2: SOURCES OF WATER........................................................................................ 3 SECTION 3: PROCESSING AND DISTRIBUTION................................................................ 3 SECTION 4: WATER PUMPS................................................................................................... 6 SECTION 5: MAINS WATER TO BUILDINGS...................................................................... 7 SECTION 6: INTERNAL DISTRIBUTION, DIRECT AND INDIRECT SYSTEMS............. 9 SECTION 7: STORAGE.......................................................................................................... 13 SECTION 8: HOT WATER SUPPLY...................................................................................... 14 SECTION 9: MATERIALS FOR PIPES.................................................................................. 16 SECTION 10: RECYCLED WATER...................................................................................... 20 1|Page UNIT 1 - WATER SUPPLY The Unit is divided into 10 sections Section 1: Introduction Section 2: Sources of Water Section 3: Processing and Distribution Section 4: Water Pumps Section 5: Mains Water to Buildings Section 6: Internal Distribution of Water Section 7: Storage Section 8: Hot Water Supply Section 9: Materials for Pipes Section 10: Recycled Water OBJECTIVES: After successfully completing this unit you should be able to: Know the various sources of water and how water is processed for distribution Know the various types of pumps and the functions they perform Discuss how water is brought to a building and how it is internally distributed and can be stored Be able to list the materials used for pipes with their properties Discuss on recycled water 2|Page SECTION 1: INTRODUCTION Water can be obtained through the hydrological or water cycle. This process occurs when evaporation of moisture from water sources occur. I.e. sea, rivers, lakes etc. These form clouds and then condensation droplets combine and fall as rain to replenish the water levels. Figure 1: Hydrological or rain cycle SECTION 2: SOURCES OF WATER The main sources of water are as follows; Underground water o Wells: wells can be classified as shallow or deep. The former refers to any well that is sunk to collect ground water. Water from shallow wells is normally unwholesome, therefore requiring treatment to make it potable. The other type of wells – deep wells, collect water from below the impermeable stratum. The inner surface of a well is lined with a suitable material such as circular pre-cast concrete sections. Dug wells for domestic use are commonly 1m to 1.5m in diameter. o Bore holes: This can be mechanized or unmechanized. The latter types are those with levers, paddles or cranks and operated with hands or legs. A borehole is formed by drilling into the ground or driving a steel lined shaft to a water-bearing stratum. The diameter of boreholes is usually between 150 to 200mm. o Springs: Springs occur naturally at junctions of permeable and impermeable stratum. The springs break where the level in a permeable stratum is above the level of the junction of a permeable and an impermeable stratum. o Waterfalls: These are similar to springs but percolate and jet along sharp cliffs or mountains. Surface water: As the name implies, surface water is obtained directly from the surface. It is usually obtained as a pool of water. Surface water sources include lakes, streams, rains collected from run off from roofs and paved areas and rivers. SECTION 3: PROCESSING AND DISTRIBUTION Water acquired from various sources need to go through a purification process in order to make it drinkable as they are polluted. A typical example is rainfall water which is contaminated by impurities (carbon 3|Page dioxide, sulphur, and nitrous oxides originating from domestic flue gases and industrial manufacturing process). A mixture of these impurities and rainfall produce ‘acid rain’. Water for drinking purposes should be clear and free from small suspended matter, colourless, free from harmful bacterial, pleasant taste and odourless. Most underground sources such as springs, deep wells and boreholes can meet the above criteria. They are therefore considered as wholesome or potable. However surface water sources cannot be considered wholesome until it undergoes some treatment/purification. In Ghana, the Ghana Water Company Limited (GWCL) is the statutory body that responsible for treatment and supply of potable water to consumers. The process of treating water starts by the collection and storage of surface water in man-made reservoirs or impounding reservoirs, the latter created from damming valleys to create catchment areas and to provide the potential for hydroelectricity generation. At this point, large materials such as pieces of stones and sticks or even dead animals are removed by a mesh. This process is known as screening. After screening, water screened undergoes other processes which are; Aeration: aeration is undertaken by exposing the water to the atmosphere. This exposure must be done in the form of a fountain. This process removes unpleasant odour from the water, increases the oxygen content and also gives that sparkle and palatable qualities to the water. Sedimentation: sedimentation is the process whereby suspended matter in water is allowed to settle at the bottom of the tank. These settle due to their weight or under gravity. In some situations, a chemical such as aluminium sulphate is added to water in the tank to facilitate the settlement process. At the Barekese treatment plant, this process is undertaken in large tanks. 4|Page  Filtration: Filtration is basically done to further remove any suspended matter left after sedimentation. Filtration removes some bacteria from the water. Filtration could be that of slow sand filter or pressure filters. In the slow sand filter, very thick layers of fine and coarse sand on graded gravel is used in an open tank. The dirty water is then introduced by an inlet valve onto the fine sand gradually sips through various layers and through the outlet as clean water. As can be deduced, this method is very slow and it occurs a large space. A faster alternative is the pressure filter. It can process water at about ten times faster than the slow sand filter. This takes place in a closed steel cylinder with pressure introduced into the tank via a compressed air pipe. It uses the same filtering materials as the slow sand filter. The rate of filtration of water using the pressure filter is between 4 to 12m³ per hour. Sterilization: The filtration process removes the suspended matter and only some of the micro- organisms. Any bacteria that survive the filtration must be killed by the use of chemicals. In this process a minute quantity of chlorine is added to classify the water as drinkable. This is what is commonly used in Ghana. Gamma rays can also be used to sterilize water. 5|Page  Softening: Two common terms, hard and soft are used to express the sense of feel of water when used with soap. Water that readily lathers with soap is considered soft. On the other hand, hardness of water means it is difficult to obtain lather with soap. Hardness can be removed by the addition of sodium carbonate or washing soda SECTION 4: WATER PUMPS In order to move large volumes both vertically and horizontally between the various treatment processes, pumps are used. The factors that will influence the choice of a pump are; 1. The volume of water to be moved 2. The rate at which water is pumped 3. The height of pumping, i.e. the vertical distance from the level of the water to the pump. 4. The height and distance to outfall or discharge point 5. The cleanliness of the water 6. The amount of noise generated by the pumping process. 7. The life span of the pump. The main three types of pumps used are; Centrifugal pump: A centrifugal pump consists of a rotary impeller, which revolves at high speed forcing the water to the sides of the impeller. The mass of water thus spins around very fast and pulls the water into its centre, forcing the water out. The pump can draw up water up to 6m. Displacement pump: The displacement pump has one or more plungers that move up and down or backward and forward, each stroke, drawing water past a valve. In other words, the action of the piston draws water into the cylinder with one stroke and forces it out with the return stroke, resulting in a strong regular delivery. Rotary pump: The rotary pump has a rotor which pockets and forces the water out. A rotary pump may be inexpensive but can wear quickly if it handles small pieces of sand. The pump can also be noisy in operation and inefficient. Submersible pump: Normally used in deep wells. It is suspended in the water to be pumped. It has a special electric motor designed for working under water. To the electric motor can be attached one or more centrifugal units. Alternatively, the displacement pump unit can be attached to the motor. After processing, water is pumped to a high-level storage reservoir water tower for distribution which can be by gravitional or pumped. 6|Page Figure 2: Gravitational distribution SECTION 5: MAINS WATER TO BUILDINGS Water mains supply a town or village maybe in the form of a grid with isolating valves. These valve enables sections to be isolated for repair and maintenance works with minimal local disruption and there is also an opportunity for water to maintain a flow. Figure 3: Ring main distribution Water mains can be divided into three categories namely; Trunk mains; these carry water from a source of supply to a district/region without supply consumers en route. Secondary mains; these are distribution mains fed from a trunk main and supply the consumers connections in the district/region. Service pipes; these branch supplies from the secondary mains that serve the individual household. 7|Page MAINS CONNECTION Connects to the trunk or secondary main is normally undertaken by the local water authority at the expense of the developer or building owner. Connections to secondary mains maybe made under pressured to connect pipes of 50mm diameter and below whereas for larger pipes, a shutdown of the main is required. An isolation stop is typically provided at the crown of the water main. Service pipes are fitted by the water supply company from the main up to the boundary of the premise after which a stopvalve is provided to enable the premises water system to be isolated from the mains. The service pipe remains the water authority’s but thereafter it is the responsibility of the building owner. A meter is also installed, preferable underground just beyond the property boundary to enable the local authority charge customers. However if this location is impractical, location within the building at the base of the rising main may be agreed with the water authority. A typical installation is as seen. Figure 4 : Typical water mains connection CONNECTION OF MAINS WATER SYSTEM The service pipe to the building should be kept at about 760 – 1350mm depth to avoid frost damage and damage from heavy vehicles. The valve pit can be a purpose made plastic chamber with key operated lid. This should be easily located for ease of access if emergency isolation is required. MAINS WATER SERVICE TO HOUSE Figure 5 shows the incoming mains water service to a building. The pipe is sleeved so that movement of the pipe or settlement of the building can take place. 8|Page Figure 5: Incoming mains water service to building SECTION 6: INTERNAL DISTRIBUTION, DIRECT AND INDIRECT SYSTEMS Cold water supply can be grouped into the direct, indirect system and combined Direct systems As the name implies, water is supplied directly to various appliances within the building. Drinking water is available at every draw off point and maintenance valves should be fitted to isolate each section of pipe work. There is no requirement for temporary storage of water in overhead tanks. This system requires a consistent supply of pressurized water which maybe difficult during peak demand periods. Can be used where there is a reliable and constant flow of water from mains. Pipe work is minimal The occurrence of back siphonage (possible negative mains pressure drawing dirty water back into the main, e.g. hosepipe attached to an outside tap with the open end submerged in a pond) is high. 9|Page  Wash Basin W.C. Kitchen Sink Bath Indirect systems This system of cold water supply requires a storage cistern (normally in the roof space) after which water is distributed to other parts of the building More expensive to install with a large cistern and almost twice as much pipework. Constant water pressure from the storage cistern which reduces the possibility of back siphonage. Preferred choice when the water main is erratic or unreliable. The reduced pressure from storage cisterns as compared to the mains pressure will usually give quieter operation. Constant supply of water Less chance of back siphonage. Tank must be cleaned regularly to avoid contamination. Water Cistern Wash Basin WC. Kitchen Sink Bath System of Water Distribution (Cistern on Roof) 10 | P a g e  Water Cistern Wash Basin Bath WC. Kitchen Sink Indirect System of Water Distribution (Cistern on Tower) Combined system As the name implies, it combines both of the systems as mentioned above. Some houses use the storage cistern as a strategic storage reserve. This means that water is supplied either directly under the mains pressure or indirectly from the storage cistern. The use of a non-return valve (which allows water to flow in only one direction) prevents the backflow of water from the storage tank. Backflow occurs when the mains pressure is lower than that of the storage tank pressure. Water Cistern Wash Basin Kitchen Sink W.C. Bath Non-Return Valve Combined System of Water Distribution WATER SUPPLY TO HIGH-RISE BUILDINGS Instances where the head of water in the main is not sufficient to supply water to the top floors of high rise buildings, there is a need to boost the water by using a pump to supply the higher levels of tall buildings. Methods vary and consultation with the local water authority is necessary to establish the most acceptable. 11 | P a g e In boosted water supply, the lower tank is fed directly from the mains. The upper floors are supplied with water from the second cistern located at the peak of the building. Water is pumped into this second tank. This is then used to supply water to the building. Supplies to various floors Valve Non-return valve Pump Cistern at peak of building Incoming service mains Cisterns fed by mains 12 | P a g e SECTION 7: STORAGE Storage facilities are mainly provided to reserve water in the likely event of interruption. This facility should be located at the highest possible location to maintain a reasonable pressure throughout the building. This is normally in the roof space of the building, though care must be taken to ensure that water is not affected by dust or debris. In large buildings however, a purposed made plant room can be created to accommodate the cistern. This room should however be well insulated and ventilated. Storage manufacturers and installers should comply with the following; Use of non-corrosive, shatter-proof materials Provide a close-fitting lid with a vent Adequate insulation Substantial support with level platform Fitting of a warning (overflow) pipe larger in diameter than the inlet Provide valves on every outlet (except warning pipe!) On large cisterns, the outlet to be opposite the inlet to encourage throughflow of water Fitting of a float valve to regulate and control the water level. COLD WATER STORAGE CAPACITY Water storage in dwellings is usually required to meet a 24 hour demand, that is, if the supply is cut off, there will be a supply of cold water for 24 hours. The consumption of cold water in any building depends upon; ▪ The use to which the water is put ▪ The number of consumers served. Figure 6 : Cold water storage tank 13 | P a g e The following design guidance are provided. Type of Building Storage per person (litres) Hostels 90 Hotels 135 Offices with canteens 45 Offices without canteens 40 Restaurants, per meal 7 Boarding School 90 Day School – nursery/primary 15 Day School – secondary/technical 20 Children’s home/ Residential nursery 135 Nurse’s home 120 Nursing or convalescent home 135 Table 1 : Design guidance SECTION 8: HOT WATER SUPPLY The temperature required for hot water is about 45˚C. Water is usually generated at a higher temperature (55˚C to 65˚C) in a vessel and mixed with cold water at mixing taps or mixing valves. It is better to store water at a temperature much higher than body temperature (37˚C) to reduce risk of bacteria growth and other water borne diseases. Hot water service systems may be divided into two main types: 1. Local systems 2. Central systems Local hot water systems is used when sanitary fittings are few and concentrated at a point. In this system water heaters are located adjacent to the fittings to be supplied with hot water. service pipe to 14 | P a g e Centralized systems have a boiler, hot water storage cylinder and a cold water storage cistern linked by supply and circulatory pipework. secondary hot water storage boil Solar heating of water In order to build a sustainable environment, solar heating of water should be considered in designs. This system occupies an amount of space usually on the roof top (which severely affects the appearance of the house) with an initial high expenditure. This can however be recouped in the long run. This system works by installing solar collectors on the roof ideally pitched at about 40˚ and facing south. This is further connected to the solar cylinder and all other associated pipeworks which should be properly insulated. 15 | P a g e SECTION 9: MATERIALS FOR PIPES Qualities of material to be used for pipes should be; 1. Durable 2. Light weight 3. Easily jointed 4. Noncorrosive 5. Impervious 6. Cost effective A good material used must last the span of the building and for easy workability, the material must not be too heavy to handle or worked with on site. The water should not react with the material thereby causing the pipe material to corrode or leak. The cost of materials used, as pipe must not be too excessive. In Ghana, the most commonly used for both cold and hot water supply services is Polyvinyl Chloride (P.V.C) and copper respectively. Aside this, galvanished mild steel pipes can also be used but are scarcely used for domestic water supply. For domestic water supply services, pipe sizes range from 12mm to 32mm in diameter. P.V.C pipes. P.V.C is strong, durable, lightweight, noncorrosive, relatively cheap and easily jointed. It also has a smooth internal surfaces and obtainable in long lengths up to 10m. Two typical jointing techniques for P.V.C pipes are solvent welded and compression joints. Copper Pipes Normally used for hot water supply. It has a smooth internal surface that readily facilitates the flow of water. They are ductile and have high tensile strength therefore can be bent cold and made into thin-walled high gauged pipes. Compression and capillary joints are two common jointing techniques for copper pipes. Mild steel pipes These are very strong and can resist damage better than other pipes. They can be used for both cold and hot water supplies. The pipes have thicker walls than copper and P.V.C, therefore heavier to handle and work with on sites. The internal surface of mild steel pipes are not as smooth as the other pipes. Screwed joints are used for connecting steel pipes. FIXING OF PIPES Water pipes may be fixed; In trenches In pipe ducts In chases made in masonry or concrete With clips The communication pipes are laid in trenches. The supply pipes which include the service and distribution pipes laid outside the building are also buried in trenches, the recommended minimum depth of trenches for water pipes is 750mm. Pipe ducts are used when water pipes are laid under floors and sometimes in ceiling. The service pipe must enter the building through a duct. Large diameter pipes, for example, 75mm 16 | P a g e are used to form the duct. Repairs and maintenance of pipe-works are made easy when pipes are laid ducts. Pipes in ducts are free from pressure from the soil and any imposed loads which may cause P.V.C pipes to deform or even crack. Masonry and concrete walls may be chased (i.e. to make a cut on the surface) for laying pipes. The walls should be chased for only small diameter pipe such as 12mm. deep chases can adversely affect the stability of load bearing walls. Where chasing wall compromise the strength of the wall, the pipes should be fixed on the wall surface by clips. Clips are also used to fix pipes on wooden and metal surfaces. PIPE FITTINGS Pipe fittings are used when pipes meet at bends, intersect at junctions or of different diameter are connected together. The three common types of fitting used are the Tee, Elbow and reducer. TAPS, VALVES AND COCKS Taps, valves and cocks are pipe-work ancillaries that control the flow of water along or at the end of a pipeline. Taps are fixed at the end of the pipeline while valves usually control the flow along the pipeline. Cocks also control the flow of water along pipelines but act faster than valves. VALVES USED FOR WATER Valves are used on water supply installations; To isolate individual sanitary fittings such as water closets, sinks and basins for purposed of repairs and maintenance. To isolate pipelines for repairs and maintenance For mixing cold and hot water On shower In storage tanks and flushing cisterns. 17 | P a g e Globe-type stop valve: this is used to control the flow of water at high pressure. Operation: To stop the flow of water, the crutch head hand is rotated slowly in a clockwise direction to gradually reduce the flow. This prevents sudden impact and the possibility of vibration and water hammer. Figure 7: Globe-type stop valve Gate or Sluice valve: used to control the flow of water on low pressure installations Operation The wheel head is rotated clockwise to control the flow of water. This valve offers far less resistance to flow than a globe valve. It consist of a metallic gate or sluice which slides vertically within a guide likely to vibrate and send tremors through the pipe work. This causes the gate to wear and unlikely to retain the ability to isolate pressure supplies. Figure 8 : Gate or Sluice valve Drain value: Has several applications and is found at the lowest point in the pipe systems, boilers and storage vessels. 18 | P a g e Figure 9 : Drain value Float valve: This is an automatic flow control device fitted in cisterns to maintain an appropriate volume/level of water Types Diaphragm: This type of float valve has a top outlet which is more preferable. Its usage is less noisy as there is less friction between moving parts. Tradition piston ball valve: are mostly found in old installations and has a bottom outlet and has a piston moving within. Legislation requires that a substantial air gap is left between the cistern’s water level and that of the float valve outlet. This installation precaution is mainly to prevent the likelihood of back siphonage if the valve mechanism and overflow fail. TAPS USED FOR WATER Taps permit draw-off of water at the end of pipes. They control the supply of water to the various sanitary appliances. They are mostly of the screw down type i.e. designed to shut off the supply gradually. BIB TAP The bib tap is used for wall fixing normally 150mm above a sanitary appliance. It is screwed directly into a fitting. A typical location example would be above a butler sink or fitted outside for use with a hose pipe connection. 19 | P a g e PILLAR TAP Used to suppy water to basins, bidets and sinks. It differs from the bib-tap in that a long vertical male iron thread which passes through the appliance and is held in position with a back-nut, the supply fed to this point below the appliance. PLUG COCKS A plug cock has a tapering plug which quickly shuts water along the pipelines. The cock can be fully closed or opened by turning the plug through an angle of 45˚ (quarter turn). SECTION 10: RECYCLED WATER The use of recycled water should be harnessed in designing. Recycled water comes from two sources ; rainwater and greywater. Greywater is the wastewater from; Sinks Baths Showers and domestic appliances. A greywater use system captures this water before it reaches the sewer (or septic tank system). Kitchen sink or dishwasher wastewater is not generally collected for use as it has high levels of contamination from detergents, fats and food waste, making filtering and treatment difficult and costly. Rainwater can be diverted from the roof drainage system to be used in other appliances. Greywater systems can be more costly than rainwater recycled systems since the water needs to be well filtered and treated to make it usable. The cheaper option in areas of moderate to high rainfall throughout the year is to recycle rainwater. 20 | P a g e