Rain Water Harvesting (RWH)

 Rain water harvesting is a self-sustainable and eco-friendly way of water conservation. It definitely acts as a tool to win over water scarcity and also helps in reducing burden from municipal water supply arrangement. Water is the basic need. In developing cities it is found that the existing infrastructure cannot match the pace of development and increasing demand of water. 

Rain water harvesting means arresting rain water during monsoon, storing it in artificial reservoirs/tanks or natural reservoirs, i.e., aquifers or using it later whenever required. Rainwater is the purest form of water. It gets contaminated during its travel either in the atmosphere or in the ground. The harvested rain water can be used for flushing, washing, gardening, irrigation - drip/sprinkler. 

In rural area, R.W.H is used for recharging of the ground water table by various methods such as percolation tanks, providing terracing on the slopes of the hill, contour bunding, contour trenching, boulder check dams and infiltration pits to facilitate percolation. 

In urban areas rainfall which occur on the roof/terrace is to be catch with the help of rain water drop pipes. It is collected to a centralised location by means of pipes. Such collected water is then used for gardening purpose, or it is directly used for recharging a bore well/ well by using filtration device to remove suspended particles/turbidity. Due to bore well/well recharging, ground water source gets replenished as well as improves the quality of ground water. It can be reused or recycled back for day to day activities by means of suitable plumbing. 

According to experts, Pune receives a total rainfall of around 700mm throughout the year. An apartment block or bungalow with 1000 sq. ft. terrace can save around 60000-70000 litres of water every year. Hardware costs for installing a rainwater harvesting system is between ₹10/12 per sq. ft. of terrace area. Approximate cost of the storage tank is ₹5 - 6 per liter of the tank capacity. 

Collection of rainwater that falls on the ground is called surface rain water harvesting. This water is polluted as it comes in contact with the ground, so it should be recharged into the ground by means of filtering recharge pits which are filled up with gravels to speed up percolation. 

Pavements:

In urban areas, people adopt paving facility around the building leaving no scope for water to percolate. To meet both the requirements one can use porous pavements made with higher % of coarse aggregates. It can also have a geotextile layer at bottom for diverting the water to particular location. P[re-cast tiles with holes at center set sand bedding will also allow good percolation. 

Sea Water Ingress:

In coastal cities, it is observed that the bore wells which initially had sweet water turn saline after some period which is on account of ingress of sea water into the soil. The sea water can also affect building foundations. Charging these wells with rain water will assure good quality of ground water. 

It is essential to collect data related to rainfall, soil analysis, water table level, water demand as per intended use and building plan before finalising RWH details. It is also necessary to do back wash of filter media around the wells for efficient functioning. Design should not cause excessive rise or fall in water table causing dampening or uneven settlements. 

Recycling of Waste Water 

Installation of water recycling system is now mandatory for all new major housing schemes. The state government notification said, "Installation of system for recycling of wastewater from bathrooms and kitchen sinks is mandatory in building layouts having net plot area, excluding area under development plan reservations, or development plan road, of 4000 sq. m. and above. The recycling system shall be installed as per the norms and specifications decided by the municipal commissioner from time to time. The treated water may be used for gardening and all other purposes other than drinking." 

Water recycling systems will help safe drinking water a priceless commodity. This scheme is useful small houses as well as new residential schemes. According to the new rule -

• Waste water (grey water) refers to water discharged anywhere in the house except in toilets and urinals. 
• Waste water can be collected in settling tanks, which ideally should be large enough to hold twice the expected daily flow plus 40% above that to allow for sludge accumulation. 
• Iodine or Chlorine can be used to disinfect water. Also various types of filters need to be used. 
• Water produced in toilets and urinals is termed as black water. As per the provisions, it would be mandatory to provide independent sewer lines to carry gray water and black water. Laying dual pipelines- one for potable and other for recycled water- would be necessary. This dual pipeline should be marked differently for easy identification.