Rainwater Harvesting

  

•  Introduction

Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. Uses include water for garden, water for livestock, water for irrigation, and indoor heating for houses etc.. In many places the water collected is just redirected to a deep pit with percolation. The harvested water can be used as drinking water as well as for storage and other purpose like irrigation.

•  Advantages

Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply. It provides water when there is a drought, prevents flooding of low-lying areas, replenishes the ground water level, and enables dug wells and bore wells to yield in a sustained manner. It also helps in the availability of clean water by reducing the salinity and the presence of iron salts.

• Makes use of a natural resource and reduces flooding, storm water runoff, erosion, and contamination of surface water with pesticides, sediment, metals, and fertilizers.

• Excellent source of water for landscape irrigation, with no chemicals such as fluoride and chlorine, and no dissolved salts and minerals from the soil.

• Home systems can be relatively simple to install and operate and it may reduce your water bill.

• Promotes both water and energy conservation.

• No filtration system required for landscape irrigation.

• Quality

The concentration of contaminants is reduced significantly by diverting the initial flow of runoff water to waste. Improved water quality can also be obtained by using a floating draw-off mechanism (rather than from the base of the tank) and by using a series of tanks, with draw from the last in series. The stored rainwater may need to be analyzed properly before use in a way appropriate to its safety.

The quality of collected rainwater is generally better than that of surface water. Contamination is always possible by airborne dust and mists, bird feces, and other debris, so some treatment is necessary, depending on how the water will be used.

• System Set Up

Rainwater harvesting systems can be installed with minimal skills. The system should be sized to meet the water demand throughout the dry season since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow. Likewise, the water storage tank should be large enough to contain the captured water.

•  Benefits

Rainwater harvesting systems are simple to install, operate, and maintain. It is convenient in the sense that it provides water at the point of consumption and operating costs are negligible. Water collected from the roof catchment is available for use in potable and non-potable applications such as toilet and/or urinal flushing, laundries, mechanical systems, custodial uses, site irrigation and for bathing water. Since rainwater is collected using existing structures, i.e., the roof, rainwater harvesting has few negative environmental impacts. 

Rainwater is free; the only cost is for collection and use. It lessens demand on the municipal water supply. It saves money on utility bills. It makes efficient use of a valuable resource. It diminishes flooding, erosion, and the flow to storm water drains. It reduces the contamination of surface water with sediments, fertilizers and pesticides from rainwater run-off resulting in cleaner lakes, rivers, oceans and other receivers of storm water.

It can be used to recharge ground water. It is good for irrigation and plants thrive because stored rain water is free from pollutants as well as salts, minerals, and other natural and man-made contaminants. It is good for laundry use as rain water is soft and lowers the need for detergents. It adds life to equipment dependent on water to operate, as rain water does not produce corrosion or scale like hard water. It can help achieve LEED Green Building Rating Credit.

 Rain water is the purest form of water. In rain water, we have total control over our water supply. It is very ideal for cities with water restrictions. It is socially acceptable and environmentally responsible. It promotes self-sufficiency and helps conserve water. Rain water is better for landscape plants and gardens because it is not chlorinated. It reduces storm water runoff from homes and businesses. It can solve the drainage problems on your property while providing you with free water.

It uses simple technologies that are inexpensive and easy to maintain. The potential cost savings especially with rising water costs. It can be used as a main source of water or as a backup source to wells and municipal water. The system can be easily retrofitted to an existing structure or built during new home construction. Systems are very flexible and can be modular in nature, allowing expansion, reconfiguration, or relocation, if necessary. It can provide an excellent back-up source of water for emergencies.

• Water Requirement and Sources of Water in Delhi

Delhi is experiencing increasing pressure to meet demand for its water resources. Growing urbanization, improvements in living standards, exploding population are just some of the contributing factors. The population of Delhi is expected to cross 15 million by the end of 2002. The city, at the moment, requires 3,324 million liters of water a day (MLD) while what it gets stands closer to 2,034 MLD. Average water consumption in Delhi is estimated at being 240 liters per capita per day (lpcd), the highest in the country. The large-scale extraction of groundwater is a result of this widening gap between the demand and supply of water. And still worse, serious doubts are also being raised about both the quality and quantity of groundwater. 

•  Physiography

The Union Territory of Delhi consists of flat and level plains interrupted by cluster of sand dunes and a long continuous chain of rocky ridges. The sand dunes are of varying dimensions and in general trend northeast - southwest. The crests of the dunes generally lie between 6 and 15 metres above the surrounding plains. They are more or less fixed in this area and support vegetation. It appears that they are of longitudinal type and are oriented parallel to the prevailing wind directions. 

 

• Drainage

The Yamuna river flowing in a southerly direction in the eastern part of the Union Territory of Delhi is the only perennial river in the area. Eastern and western Yamuna canals and Agra canal are the three major canals which originate from the Jamuna river with Bawana, Rajpur and Lampur distributaries. Auchandi, Budhanpur, Sultanpur Mundka, Mongolpur, Nahari, Dhansa and Surkhpur are some of important minors. The Agra canal originates from Okhla, about 12 km. South of Delhi.

• Delhi receives its water from 3 sources:

A. Surface Water:86% of Delhi's total water supply comes from surface water, namely the Yamuna River, which equals 4.6% of this resource through interstate agreements.

B. Sub-surface water: Ranney wells and tubewells. This source, which is met through rainfall (approx. 611.8 mm in 27 rainy days), and unutilized rainwater runoff, is 193 MCM (million cubic meters).

C. Graduated Resources: It is estimated at 292 MCM, however current withdrawal equals 312 MCM. Salinity and over exploitation has contributed to depletion and drastically effected the availability of water in different parts of the city. However, according to a report released by the Central Ground Water Board (GCWB), Delhi's ground-water level has gone down by about eight meters in the last 20 years at the rate of about a foot a year.

Apart from groundwater, Delhi gets its water from the Ganga Canal, the western Yamuna canal, the Bhakra canal and the Yamuna.  

 

Delhi’s water and wastewater management is controlled by the Delhi Jal Board (DJB), which has signed the contract with Suez Degremont. With the demand-supply gap projections for water set to increase in the next ten years, DJB have identified new raw water sources including Tehri, Renukal, Kishau Lahawar dams. Plans also center on the construction of new and existing sewage treatment plants (STPs), which will enable an increase in treatment capacity. Rainwater harvesting is another option that DJB is considering.

Even though Delhi is one of the first Indian cities to have paid attention to city planning with the first master development plan of 1962, the infrastructure for public utilities is proving to be inadequate, especially under the burden of growing population.

Delhi has total area of 1486 sq kms out of which fully developed urban areas is 525 sq kms. With over 14 million inhabitants, the city is bursting at its seams. Population of Delhi is expected to reach 17.5 million by the end of the 10^th Five year plan. Situated on the banks of the river Yamuna, the city is mainly supplied by surface water from the Yamuna, Ravi beas water ( Bhakra storage) and the Ganga water. The water availability from surface water sources, viz. Yamuna, Ganga and Bhakra systems is approximately 1150 MCM ( million cubic metre), and of  this 60 % is available from Yamuna river.Total groundwater availability is of the order of 290 MCM per year. Delhi receives a total average rainfall of around 600 mm per year, of which 80 % is received in three months ( July – September).