Water demand for an increasing population has to be met from a suitable source. This source should be able to suffice the requirements in term of quantity as well as quality of water. The usual sources for supply of water such as rivers, lakes, ponds and canals have their own arrangement of collecting water that may or may not depend on any external sources for the full or partial supply of water.
What are the various sources of water for human consumption?
- Surface water: this refers to the water that is available in rivers, lakes and other fresh water lands. Surface water naturally replenished over time with precipitation and is naturally lost due to evaporation. Even though the only natural input to any surface water source is precipitation within the watershed, it can be depleted due to sub-surface seepage and evaporate-transpiration as well. Thus, the total amount of water in these sources is constantly changing and is based on various external factors. These factors can include storage capacity of lakes and artificial reservoirs, permeability of soil that is beneath these storage bodies, timing of precipitation and evaporation levels.
Human activities can large contribute to these factors such as an increase in pollution levels to the surface water that may make it unfit for consumption. - Ground water: This largely refers t sub-surface water that is fresh water which is located the pore space of soil and rocks below the surface of earth. Water that flows within aquifers below the water table is also included in this. The main difference between sub-surface water that is associated with surface water and deep surface water in an aquifer is the unsustainable usage of sub-surface water in the long run.
Across the country the most common source of water is underground water that can be extracted with the use of bore wells and tube wells.
High capacity bore wells use a casing pipe of 10 to 12 inches in diameter and have a depth of over 80 meters. Medium Capacity bore wells generally use a casing pipe of about 8 inches in diameter and are over 50 meters in depth but less than 80 meters. A low capacity bore well uses a casing pipe of 6 inches in diameter and has a depth of 30 meters to 50 meters.
The design and selection of size of opening and length of the bore well is an extremely important factor to be kept in mind. This directly affects the quantity and quality of water and service life of the bore well. Coarser formations in aquifers require very large grain sizes to filter median and a large opening the screen. However, smaller formations require a smaller size of filter media and small openings in the distribution and formation of the aquifer.
Bore wells in coarse grained strata such as sandy graves can be developed naturally as there is no need to develop a filter pack. This is the most common expenditure that can be avoided which creates a negative impact on the development of the well.
Generally slotted casing pipes are used as a screen. These screens have a small open. Wire wound continuous screens provide large slot areas without the loss of strength of the pipe that are now commonly used for high capacity bore wells. MS casing pipes and screen should not be used in case of corrosive aquifer conditions like high levels of chloride, TDS, hydrogen sulfide etc. as they may lead to corrosion and damage.
The screen portion is often kept for too long in most of the bore wells and almost cover one-third to two-third of the depth of the bore well. Thus it is advised to keep the screen in the deepest parts of the bore well.
Screen extending which is very high in bore wells can largely affect the development of graded zone and can also increase the contamination levels as the water from higher levels will tend to flow into the well through the space filled with gravel.
There should be an organized system of transporting and passing important elements such as casing pipes, screens and pea gravel that is to be used in the construction of bore well as this work is completely hidden work performed under ground level. It is not possible to check the quality and functionality of materials that are used post construction.
Proper bacterial and chemical analysis of the bore well water should be performed regularly to ensure that the water is fit for human consumption. Post installation the aquifer should be developed and maintain to prevent any repairs and damages. The bore well can be disinfected before being used with the help of shock chlorination. The estimated of bore well yield and pump capacity should be correctly analyzed by draw downs and recovery curves from pumping tests.
The bore well should also be used immediately after instillation. The common practice of providing the pump house right above the bore well will delay the commissioning and pumping testes that are essential by several days or even months at times. This can be avoided by creating a room for electrical control panel and installing a chlorination plan at a short distance from the bore well.
Aquifers:
There are various layers of solids and rocks below the water table that can broadly be classified as aquifers and aquicludes. Aquifers refer to water bearing layers that provide water to wells in usable amounts. The most common form of making aquifers is by the use of stone, sandstone and gravel. A combination of these materials can help create large interconnected space between grains that the water can move freely. Shale and coal can also be used for this purpose if they are fractured enough and ensure that water is allowed to move freely through them.
Aquicludes refer to water formations that cannot yield adequate water for wells. The most common aquicludes are un-fractured coal and shale. The pore spaces between the grains of such materials are extremely small that the water moves very slowly.