Fresh water found on land has only two primary sources - melting of ice, and rain. Harvesting rain is crucial for sustaining both the surface and sub-soil water sources. That this has been well understood throughout rural India historically is evident from the numerous age-old water harvesting systems put in place several decades ago, which operate even today.
60% of India is expected to be living in towns and cities by 2025. The logical extension of a burgeoning population and urbanization is the conversion of open spaces into paved ground. This has resulted in flooding of cities as well as water scarcity due to groundwater depletion and the lack of rainwater harvesting.
While rural harvesting is mostly traditional and is carried out in surface storage bodies like rivers, tanks, ponds and lakes, urban harvesting, due to lack of open space for capturing the runoff, is mostly in sub-soil storage as groundwater recharge. This recharge is facilitated by open wells, recharge wells and recharge pits, which send the water right into the ground.
How do you harvest rainwater?
The easiest way to harvest rainwater is to divert the rain that falls on the terrace into open wells. Open wells tap the water at shallow reaches and serve as conduits for the water to spread and permeate underground when rainwater is fed into them. This helps keep the shallow water table in good health.
In the absence of an open well, a percolation/recharge well could be dug within the premises to inject rooftop rainwater into it for groundwater recharge. A recharge well is usually around 10-15 feet deep and its depth depends upon the nature of the soil underneath and the volume of water it is expected to receive during a heavy downpour.
In the case of huge apartment complexes where the space around the built-up area is considerable, plans should be drawn up to harvest the water that falls around the building. This could be done by installing a simple 'gate trap' which traps all the water that flows out of the building. Since the water may contain a high amount of suspended material, it not not advisable to divert this into an open well. A smaller percolation or recharge well may be constructed for the purpose.
Harvesting rainwater not only takes care of immediate water needs, but also ensures a greater degree of certainty in terms of improved groundwater quality and quantity for the future.
Over 50% of the daily water usage of households occurs in kitchens and bathrooms. Contrary to popular belief, refuse water from bathrooms and kitchen is excellent quality used water which can be re-used.
Before underground sewerage was introduced in most cities, water followed a cyclical route. Water was drawn from dug wells within the premises. Refuse water from the bathrooms and kitchen were let out into the garden while water from the closets reached septic tanks. The soil treated the greywater and sent it back into the ground, thereby closing the household water consumption-reuse loop.
The advent of piped underground sewerage has drastically changed the scenario in over 200 towns and cities in India. The greywater (sullage) gets mixed along with the blackwater (sewage) from the toilets. Water which has the potential to be re-used for non-potable puposes such as gardening or flushing is simply led out of the plot to be treated several kilometres away in centralized facilities, the fate of which is questionable.
Instead of mixing sullage with sewage, we can effectively recycle this used water. A simple process involving plants, soil and sunlight can get rid of most of the organic material in greywater.
To do this, the first step is to ensure that the pipeline from the bathrooms and kitchen do not join the underground sewerage line. This water can then be diverted into a bed of water-loving Canna plants. These plants take up organics from the used water and the soil bacteria further polish the water as it moves deeper underground.
Putting this in place will help reduce the load on external sewage treatment systems and recharge the ground, thereby replenishing the water table below.