Rainwater harvesting in India has a number of benefits:
- 1. Householders and non-residential buildings can acquire independent supplies of both potable and non-potable (i.e. for washing, etc.) water via harvesting and use of water-stores
- 2. Natural aquifers can be artificially recharged: that is, instead of rainwater entering storm drains, it can be directed to bore wells, pits, etc. which will connect to the aquifers. This is especially important in Northern India, where aquifers are significantly depleted.
- 3. Reduction in flooding: a major concern in Indian cities such as Delhi!
Basics of a rainwater harvesting system
- First, let's look at the essential elements of a rainwater harvesting system for domestic or non-residential building usage. These comprise: a roof, a water store, and piping/guttering to lead the rainwater from the roof to the water store! The roof should preferably be made of hard non-polluting non-absorbing material (not asbestos!): tiles, metal sheets, and plastics would be suitable. The water stores can be placed above- or below-ground, with the first option being lowest cost. The stores are commonly plastic, clay, ferrocement, or concrete.
- We can make the rainwater harvesting system more effective by adding more components: filters (including 'first-flush systems' which remove the first few litres of rain from the system), overflows, level gauges, pumps (to move the water from our store to elsewhere), leaf screens, valves, UV filtering (to kill viruses and bacteria which may inhabit the water store). In addition, rainwater can be sent to to wells -- either directly or via overflows from water stores -- in order to replenish naturally occurring aquifers. Examples of more advanced systems are shown below:
- Contamination warning!! Whilst rainwater is in itself clean, there are several points in the system at which contamination can occur: rain falling in a polluted atmosphere may collect pollutants, chemicals on roof, microbiolgical contamination on roof (e.g. via insect and bird vectors), microbiological contamination in water store (via various vectors such as insects and rodents and humans!), chemicals entering tank, etc..
One thing I would like to touch on in-brief before we move on, is that roofs are not the only potential source for rainwater harvesting! We actually have another structure which could be useful: ROADS!!
- Could roads provide rainwater to recharge aquifers?
Rainwater Harvesting in Delhi
: Let's think about just how much water we can potentially harvest - taking into account rainfall of Delhi!
- The climate of Delhi is monsoon-influenced humid subtropical (Köppen climate classification Cwa) bordering semi-arid, with high variation between summer and winter temperatures and precipitation. Delhi's version of a humid subtropical climate is markedly different from many other humid subtropical cities such as Sao Paulo, Tokyo and Brisbane in that the city features dust storms (something more commonly seen in a desert climate), has relatively dry winters and has a prolonged spell of very hot weather, causing it to be also classified as semi-arid region.