Rainwater harvesting has been acclaimed as an exemplary method of water conservation, and is considered to be a “Green Practice”. It involves the collection of rainwater from rooftops or other hard surfaces above the ground level prior to its loss as surface run-off. This method of water conservation indirectly supports the replenishment of groundwater and compensates for the exhaustion of non-potable water.
Rainwater harvesting is an effective method of dealing with the water crisis that inevitably occurs in developing countries like India, Indonesia, Philippines, Malaysia, Sri Lanka, South Africa etc.. It can help to alleviate the water shortage in urban India to a large extent with proper management and investment.
What is the need for rainwater harvesting?
- Paucity of water:
As population and human settlements increase, there has been an exponential rise in the demand for water. The result is a depletion of water in groundwater tables and reservoirs. As Population is increasing it increases pollution in existing water sources as well, leading to possible threats to health and wellness. Moreover, water availability from natural sources like lakes and rivers varies greatly. These seasonal variations can be mitigated through the collection and storage of rainwater.
- Protection of natural water sources:
Reliance on rainwater for household and industrial needs aids in the rejuvenation of underground water. It can also prevent flooding and water stagnation in flood-prone areas during monsoons. Simultaneously, coastal areas are also protected as the dependence on sea water naturally reduces. Rainwater harvesting promotes rainwater infiltration into the subsoil, improving the vegetation cover and agriculture as well.
What are the advantages of rainwater harvesting?
- Economical, accessible and convenient:
Rainwater harvesting is a simpler procedure to access water. Natural water sources that are traditionally utilized may be at a great distance from the place of residence, especially in rural India. The storage of rainwater at home improves accessibility to clean water, thereby creating a positive impact on health. Rainwater harvesting is more economical than the inadvertent exploitation of groundwater sources. Moreover, it helps to recharge groundwater tables and natural water sources. Aquifers may be used to distribute water to places that are at close quarters, which will reduce the loss of water during transport as well.
- Simplified mode of water collection and storage:
There is no government assistance or elaborate technical knowledge required for rainwater harvesting. Only traditional methods are employed for this method of water collection.
- Unification of the community:
Rainwater harvesting can bring the community together to work in harmony towards achieving the common cause of water conservation. It can be made into a group effort that benefits the society at large and impacts every household positively. Rainwater harvesting systems can be constructed with basic training and at minimal cost.
- Hygienic, dependable water source:
A scarcity of groundwater leads to dependency on possibly polluted water sources that may be contaminated by human or animal wastes. Rainwater is generally hygienic, good quality and may be consumed without a lot of processing. Rainwater can also be maintained better than centralized piped water supply, as its cleanliness level can be controlled by the individual tank owner.
Considerations for Rainwater Harvesting
Rainwater harvesting should be considered when:
- Groundwater has a high iron or fluoride content
- Groundwater is brackish
- Four months prior to the monsoon season
- Increased water demand domestically, industrially or commercially.
Important Components of a Rainwater Harvesting System
Catchments may be rooftops or land surfaces that act as the collection point for rainwater. Rooftops should be tiled, tin or cement. Land surfaces can be paved, unpaved or semi-paved. Smooth surfaces result in more rainwater run-off whereas unpaved surfaces absorb more water.
Depending on where they are located, catchment areas are prone to contamination. In industrial regions contamination maybe from toxic waste and in highways and roads, oil and grease are likely sources.
- Pipes and gutters:
Downtake pipes or gutters transfer water from catchment to the storage tank. Gutters are horizontal channels around the sides of a roof. The material used for pipes and gutters may be galvanized iron, steel, PVC, bamboo or betel trunks.
- Filters and first flush devices:
These useful devices divert the water from the first rains, which are usually polluted, and prevent them from entering the storage tank or recharging units. The first 2.5 mm of rainfall is generally flushed away by first flush devices. This amounts to fifteen to twenty minutes of the first rain or few showers.
- Storage reservoir:
Storage reservoirs have a tap or pump to access the water and may be above or below the ground level.
- Delivery system:
These are pipes that convey rainwater to the point of use.Rainwater collected through this system can be used to replenish depleting groundwater level by redirecting it to aquifers through bore wells, recharge wells or recharge trenches.
Technical factors required prior to setting up a rainwater harvesting system:
- Impervious roofing such as iron sheets, tiles, and cement
- Storage tank space of at least 1 metre square in close proximity to each house
- Knowledge of the rate of water consumption and the amount that needs to be stored
- Alternative water source which is useful when rainwater is exhausted
- Sourcing labourers with technical knowledge and skill
- Gaining access to required construction materials
The Amount of Water that can be Collected Through Rainwater Harvesting
There are many factors which influence the amount water that can be collected through the process of rainwater harvesting.
The average annual rainfall in the past 10 – 25 years, its peak intensity determines the potential of rainwater harvesting in a particular area.
An approximate amount of water that can be collected can be found using a mathematical formula to gauge the potential run-off as follows:
Run-off coefficient depends on the type of catchment area that is present. It can range from 0.0 for the soil to 0.95 for an impermeable concrete pavement.
Rainwater harvesting is an ideal and effective method of water conservation. Industrialisation and unsolicited dumping of toxic wastes into natural water bodies have contaminated them, rendering them unfit for human consumption. Rainwater harvesting is not only cost-effective, it is also easy to put into practice especially when time, effort and money are invested by the whole community at large. Rainwater harvesting has immense potential to reduce the global footprint and preserve ecology for the coming generations and should be given top priority by every environmentally conscious citizen.Run-off coefficient depends on the type of catchment area that is present. It can range from 0.0 for the soil to 0.95 for an impermeable concrete pavement.