Rain Water Harvesting - an imminent necessity

My mother remembers being able to feel the water in a well by just lowering her arm into it. This was the situation decades back in a water-well in my cousins’ place, right beside our house in Cuttack. Today, the well has water a few feet below; this being in a city surrounded by two rivers. Ground water depletion is not alien if you are living in bigger cities like Chennai, Bangalore, Delhi, etc. In Bangalore, 800-1000 feet depth is the norm of new bore wells in most areas. 20 years back, a 150 feet bore well was sufficient to get water in that area. Rampant usage and removal of rain water harvesting sites like lakes and ponds are the causes of this. Ponds being replaced with high rises are a common sight in every developing city. 

more than 200 days of free swach water considering Kejriwal’s 700 litre per day use. Imagine the amount of rainwater wasted every year.

What is ground water? 

Ground water is the rain water percolated in the earth’s porous surface. Consider the surface below us a huge water storage. The top soil layers (sand, silt, gravel) are porous. Rain water gets absorbed through these and moves down by gravity till it reaches an impermeable surface rock or cracks in such rocks. The rain water saturated in this region can be extracted for use by drilling a well. These water bearing rocks or unconsolidated materials (sand, silt, gravel) are referred to as an aquifer. The depth at which aquifers are found depends on the geology of the place and amount of rainfall it receives. In rocky high altitude Bangalore, the water table lies much lower than the riverbed city of Cuttack where bore wells of 100 feet can suffice. Bhubaneswar, the twin city of Cuttack, has a lower water table too owing to its slightly higher altitude and distance from big rivers. Apart from that, rampant construction has lead to ground water shrinkage in the capital city. New bore wells have average depths of more than 200 feet here. Well it is undeniable that dry aquifers can lead to catastrophic effects on human civilization; storm water off buildings and roads causing flash floods, or dry wells aiding water tanker mafias. 

The percolation pit and recharge well are functionally similar to a soak pit.

What can be done to recharge the ground water? 

Ground water has depleted because rain water has not been allowed to enter the aquifers. In urban areas, there are a few ways to recharge the ground water. One of the simplest ways is rain water harvesting off the surface of buildings instead of letting it run off in the storm water drains. Storing the rain water in underground tanks/sumps or drums is very effective. Rain water is one of the purest sources of water. However, the roof surface must be clean enough to ensure that this water is potable. A simple mesh filter is often enough to use this water for most purposes like cleaning, washing, bathing, etc. This directly reduces your water consumption. Rain water is water filtered to perfection by nature. When this water reaches polluted rivers or streams via storm water drains, it gets contaminated. Pumping and treating this water back to houses is wastage of huge amounts of energy. Soak-pits are another simple way of recharging ground aquifers. A soak-pit is essentially a small dug out pit lined and layered with permeable materials like sand, coal, gravel, etc where rain water is allowed to flow, get absorbed and filter into the aquifers. A small soak-pit of 4x4x4 (feet) dimension can do wonders to increasing your ground water level. Larger the soak-pit, greater is the water absorbed. 

Aquifer

Another important way is recharging your bore well directly with the rain water. This process involves adding filters to the rooftop storm water discharge pipe. Every defunct bore well should be fitted so. Alternatively, one can dig up a soak-pit near the bore well. This would filter the water better and prevent clogging but a lot of water would have to be diverted away as its capacity & filtration rates are low. 

How much water can be collected? 

Rain water collected = Area of catchment (roof) X Total rainfall in a year. For Bhubaneswar, which receives around 1500 mm of rain every year, the rain water that can be collected from 100 square meters roof is 150000 litres. This means more than 200 days of free swach water considering Kejriwal’s 700 litre per day use. Imagine the amount of rainwater wasted every year. 

Rain water harvesting needs to be implemented both on the individual and organizational level. The government needs to introduce laws which mandate rain water harvesting in every building and plot of land. Some states in India have laws for bigger buildings. Apart from that, community and public rain water harvesting projects can be undertaken to improve ground water levels. Soak-pits or recharge pits by the side of roads can immediately reduce chances of flash floods while recharging dried aquifers below. High rise buildings, where consumption is high per unit area, can greatly benefit from rain water to bore-well recharges. According to a recent report, 80% of surface water in India is contaminated. Water is extremely precious; we have to start caring immediately. 

Paint the town white!

Summers are getting hotter. Air Conditioners are expensive. So are energy bills - which makes ACs un-affordable for many. Painting the roof white is a low cost solution to beat the heat relatively. This is for rooms and spaces where the roof is exposed to direct Sun light. A little bit of tech gyan first. Heat and light from the Sun travel together. A body is black in color because it absorbs all light falling on it. Hence it absorbs all heat too. A white body on the other hand reflects all light (and so heat) falling on it. In simple words, white is coolest, black is hottest. A dark concrete roof absorbs and transmits a lot of heat during daytime and also radiates during the evening. On the other hand a reflective surface like white painted roof reflects away the light and heat and is often several degrees cooler. Indoors can become 10-15 degrees (Celsius) cooler after being coated with white paint. The hot oven-like feeling on entering rooms during afternoon and evening can be eliminated using this technique. For buildings having air conditioning, energy bills will reduce as it takes lesser energy(also less power plants, less CO2) to cool a cooler room than a hot one. 

White roofs can also help reduce global warming too. According to a research by Department of Energy, USA, white roofs not only reduce air conditioning loads of a building but also help reflect back the solar irradiation back to space. Darker surfaces on the other hand absorb the heat during Sun shine, and radiate it afterwards making cities and the surroundings hot. This is urban heat island effect. These radiations being in different wavelength than the ones incident are not rejected back to space. Studies suggest that if roofs of all buildings in the whole world are painted white, global warming can be reverted. Yes, lower energy bills, a comfortable interior & also saves the environment.

The options:

White paints come in different forms. Traditionally limestone(choona) mixed with adhesive is available commercially in India. Lime is cheap and easy to apply. Other alternative is white cement paint, which is affordable and also is slightly better in resisting rains than lime. Do note that these two paints have to re-coated every year. Another alternative is elastomeric paints. Some Indian brands like ICI Dulux and Berger Paints sell it. These paints form a rubber like stretchable membrane on the surface and are highly resistive to rains. It can last 3-5 years. The downside is that it costs a lot, generally 20 rupees per square feet area. In contrast, lime and cement paint come at around just 1-2 rupees per sqft including labor charges.  

A permanent but expensive alternative is white ceramic tiles. They come at 50-60 rupees per sqft at the least. They can last a lifetime and are much easier to clean, and your terrace looks beautiful too. The roof can be water proof too if grouted properly. It provides an all year cooling as paints are usually washed after rains, and in our tropical climate, we often need air conditioning for more than 6 months in the year. Any white surface (both paints and tiles) provide a longer life to the roof, as expansion and contraction due to heat is greatly reduced. Crack formations are minimized too. Solar Reflectance Index (SRI) values on commercial products are a good way to compare - higher the better. For tiles, vitrified variety is better suited to outdoors due to lower water absorption capacity. 

White is the new green. Cars too in white color save fuel as compared to black ones. Yes your walls and everything exposed to Sun is better off in white. We do white cement paint every year and it is a big relief in this sultry Odisha heat. We have temperatures touching 45 degrees Celsius every summer. White paint works beautifully here. Let us know if you have done it, your experience or any questions if you have - we will be happy to answer them. So cool interiors, climate change arrest, longer roof life – when are you going white?