Tales Behind the Tap - 1
Water. It is a thing which so many of us reading this take for granted. Just open the tap, and it starts flowing. When you have taken enough, close the tap. Simple.
So here is a look at what goes into getting that water to your tap.
Once the treated water is available in the proximity of the end use area, a network of pipelines is laid out according to the population concentrations within the end use area. The demand (volume used per unit time) for water is also taken into consideration, as the demand is typically much higher in the morning hours compared to the rest of the day as people do their daily activities in the morning.
Systems can be broadly divided into two types – limited duration supply in which water is provided to the end users for only a few hours a day or on alternate days or other such time restrictions, or 24-hour supply in which the end-use distribution is carried out continuously. There are a number of points to be considered for comparing these two systems such as delivery pipe size and cost, storage requirement, pump design and their energy and operating costs etc.
Gravity-based systems are those in which large volumes of water are stored at some high-elevation reservoirs and then the downhill flow is used to supply this water to the end users. The feasibility of such systems is highly dependent on local topography.
When gravity-based systems cannot be set up or are otherwise insufficient, pump houses are established at a number of locations within the distribution area as per requirement. The treated water is initially fed to and stored in these pump houses and from here it is pumped to the end users or into overhead tanks as per the decided schedule or as per requirement.
From the pump houses/storage tanks, water is initially pumped out through relatively large pipes, and the pipes become smaller in size as they approach the point of end use. The connection provided to the end user is often specified using the pipe diameter, which is decided based on the type of end usage (residential/commercial) and the water requirement fulfilled. In large commercial complexes or multi-storied buildings, the design of the pump/overhead tank used for bringing the water to that location may not be able to deliver the water to the top of the building. In such cases, the water is stored in a tank inside the premises and is handled by a dedicated pumping system controlled by the building/complex.
All parts of the water supply system – the pipelines, valves, the pumps and motors, the pump house buildings and storage tanks – have a limited useful life and require continuous maintenance. The useful life is relatively long – it is considered as 15 years for pumping machinery and 30 years for the civil structures. This is a long duration which is often sufficient for significant changes in population as well as infrastructure development. Some of these points are factored into the design itself, such as estimating the population after 15/30 years based on historical data, and designing the system according to this requirement.
Part 2 deals with the problems being faced in water supply systems and how people can do their bit.
So here is a look at what goes into getting that water to your tap.
How a water supply system is designed
The major factors taken into consideration while designing a water supply system are population of end users, location of water sources, topography of land from the water source to the end use area and within the end use area, and water quality.
As per Indian standards, the water requirement at point of end use is 135 litres per person per day (referred to in technical documentation as LPCD, or litre per capita day) for residential use. This figure includes uses such as bathing, flushing etc. Similarly there are norms determining water requirement in commercial buildings, factories, hospitals etc. Some losses are expected to take place during conveying the water from the source to the end use and these are factored in at the design stage. The population thus determines the amount of water expected to be drawn from the source.
Location and topography are important considerations for designing the pipelines for transporting the water. Longer distances and uneven land surface result in requirement of longer lengths of pipes. This not only increases the cost but also increases the energy loss due to friction between the flowing water and the inside of the pipe. Also, more elevation at an intermediate point in the system means that more effort will be required to first deliver the water to that high elevation point, from where gravity may be used for supplying it further. Both the elevation and the friction loss are essential considerations in the selection of pumps for pumping the water, and also affect the energy consumed by the pumping system for supplying the water.
The water has to meet some quality requirements, such as hardness, colour, levels of certain chemicals and microbes etc. to be considered fit for use by humans. Normally, the water source is a water body such as a river, dam or lake, and the ‘raw’ water at these sources does not satisfy these quality requirements. Thus, depending on the raw water quality, a plan is prepared for treatment of the water so that it meets the required standards. This plan consists of deciding the various processes and chemicals/materials which will be required to improve the quality of the water to required standards.
Raw water pump houses and clear water pump houses at water treatment plants often have large sized pumps having high design flow rates. They are commonly used to transport in bulk a large portion of the total amount of water required for a city or a cluster of smaller settlements located close by. The electricity consumed in transporting such high volumes of water can easily cost millions of rupees in a single month.
Large, high flow rate pumps installed in a pump house. A person standing near the pump gives an idea about the size.
As per Indian standards, the water requirement at point of end use is 135 litres per person per day (referred to in technical documentation as LPCD, or litre per capita day) for residential use. This figure includes uses such as bathing, flushing etc. Similarly there are norms determining water requirement in commercial buildings, factories, hospitals etc. Some losses are expected to take place during conveying the water from the source to the end use and these are factored in at the design stage. The population thus determines the amount of water expected to be drawn from the source.
Location and topography are important considerations for designing the pipelines for transporting the water. Longer distances and uneven land surface result in requirement of longer lengths of pipes. This not only increases the cost but also increases the energy loss due to friction between the flowing water and the inside of the pipe. Also, more elevation at an intermediate point in the system means that more effort will be required to first deliver the water to that high elevation point, from where gravity may be used for supplying it further. Both the elevation and the friction loss are essential considerations in the selection of pumps for pumping the water, and also affect the energy consumed by the pumping system for supplying the water.
The water has to meet some quality requirements, such as hardness, colour, levels of certain chemicals and microbes etc. to be considered fit for use by humans. Normally, the water source is a water body such as a river, dam or lake, and the ‘raw’ water at these sources does not satisfy these quality requirements. Thus, depending on the raw water quality, a plan is prepared for treatment of the water so that it meets the required standards. This plan consists of deciding the various processes and chemicals/materials which will be required to improve the quality of the water to required standards.
Raw water pump houses and clear water pump houses at water treatment plants often have large sized pumps having high design flow rates. They are commonly used to transport in bulk a large portion of the total amount of water required for a city or a cluster of smaller settlements located close by. The electricity consumed in transporting such high volumes of water can easily cost millions of rupees in a single month.
Large, high flow rate pumps installed in a pump house. A person standing near the pump gives an idea about the size.
The final stage – Delivery to the end users
Systems can be broadly divided into two types – limited duration supply in which water is provided to the end users for only a few hours a day or on alternate days or other such time restrictions, or 24-hour supply in which the end-use distribution is carried out continuously. There are a number of points to be considered for comparing these two systems such as delivery pipe size and cost, storage requirement, pump design and their energy and operating costs etc.
Gravity-based systems are those in which large volumes of water are stored at some high-elevation reservoirs and then the downhill flow is used to supply this water to the end users. The feasibility of such systems is highly dependent on local topography.
When gravity-based systems cannot be set up or are otherwise insufficient, pump houses are established at a number of locations within the distribution area as per requirement. The treated water is initially fed to and stored in these pump houses and from here it is pumped to the end users or into overhead tanks as per the decided schedule or as per requirement.
From the pump houses/storage tanks, water is initially pumped out through relatively large pipes, and the pipes become smaller in size as they approach the point of end use. The connection provided to the end user is often specified using the pipe diameter, which is decided based on the type of end usage (residential/commercial) and the water requirement fulfilled. In large commercial complexes or multi-storied buildings, the design of the pump/overhead tank used for bringing the water to that location may not be able to deliver the water to the top of the building. In such cases, the water is stored in a tank inside the premises and is handled by a dedicated pumping system controlled by the building/complex.
All parts of the water supply system – the pipelines, valves, the pumps and motors, the pump house buildings and storage tanks – have a limited useful life and require continuous maintenance. The useful life is relatively long – it is considered as 15 years for pumping machinery and 30 years for the civil structures. This is a long duration which is often sufficient for significant changes in population as well as infrastructure development. Some of these points are factored into the design itself, such as estimating the population after 15/30 years based on historical data, and designing the system according to this requirement.
Part 2 deals with the problems being faced in water supply systems and how people can do their bit.
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