Maintenance- the following steps should be adopted to ensure quality of harvested rain water:
Keep all catchments neat and clean
Don’t allow contaminated water to flow into system
Put iron/nylon mesh/fine cloth on inlet and outlet pipes and chambers to prevent solid debris from getting into the system
Clean open drains regularly by removing deposits of sand and gravel
Make available a layer of soil beneath the recharge structure to ensure natural filtration
Drain and clean storage tanks thoroughly before every monsoon
Change the filter media every year
Remove algae from the roof tiles and asbestos sheets before the monsoon
Do not let water stagnate in the collection chamber since this will slow down the recharge of water
Repair cracks in ferrocement tanks
Impact assessment will help you answer the following questions:
Will RWH improve the water levels?
Will it increase the water availability in the existing bore well?
Will it reduce the water logging?
Will it improve water quality?
Who is going to be benefit?
Monitoring for quality- Quality of water harvested can be monitored by sending water samples to labs for testing or using easily available water testing kits.
Monitoring for quantity- Monitoring quantity of rain water harvested will help you provide concrete evidence of the impact of rainwater harvesting. If the data is positive it will help to catalyse other people to follow in your footsteps. A monitoring system will help determine:
how much rain water are you catching
how much of the rain water harvested are you using
how much are you recharging
Groundwater recharge ratecan be calculated using water level monitoring or infiltration test. It is recommended that the monitoring be done monthly especially pre and post-monsoon. If ground water is being extracted monitoring extraction from tubewell will give you total extraction based on the formula = Hours of pumping X yield of tubewell
Using a water level indicator- The water level indicator consists of a probe, a graduated cable or tape, and a cable reel with built-in electronics. The probe is lowered down the standpipe until a buzzer indicates contact with water. Depth-to-water measurement is read from cable or tape. Regular monitoring will show trends for the impact of RWH. It takes few years to show tangible outputs.
Infiltration or recharge rate test- A simple test to know the exact recharge rate from the recharge wells. Use a water meter to measure the level of water flow into the recharge tank followed by continuously monitoring of the level of water in the tank.
CSE has been regularly monitoring water levels in all its model RWH projects. It was found that in places where rainwater harvesting was undertaken, the water levels had not declined. In the same period, there was a general decline in the water table in the areas of Delhi where the model projects were situated.
In order to monitor the quantity of water being used, the following audit should be carried out:
Gather information on where you are getting your water from (municipal, groundwater, tanker)
Find out what is your total water requirement.
How much of this demand are you getting from your supplies.
How do you use your water (drinking, cooking, bathing, washing utensils & clothes, toilet requirements, gardening, other miscellaneous such as car wash, courtyard wash)
Identify all possible avenues for reduction of use.
Identify priority or most effective use for harvested rainwater