Rainwater Harvesting in Urban areas

"The ideal solution of depleting ground water resources in India is water harvesting system." How it can be made effective in urban areas? [UPSC MAINS 2018]

The urban areas are not only the largest users of freshwater resources but are also the biggest contributor towards freshwater crisis. The increasing population in urban areas has put tremendous pressure on the freshwater resources. Today the demand to supply freshwater for domestic use far exceeds the capacity of nature to replenish the groundwater aquifers, thus resulting in the scarcity of water in the urban areas.  The taps and wells are running dry and people waiting for hours in long lines for the water tankers to arrive have become a common sight in many metropolitan cities.

Water scarcity in Urban areas   

If in older days someone would have said about buying water, people would have mocked him. But today in 21st century, purchasing water has become a harsh reality as well as our need.

The hand pumps and water taps are running dry as water table has depleted and people have to wait in long queues for hours to collect water from water tankers or public taps during summers or purchase packaged water.

The government tankers take 2 to 3 weeks to arrive, so people have to rely on private tanker mafias to supply water who charge as they wish.

The government is trying to supply water through train with water bogies to distant off places where people wait anxiously for water to arrive to quench their thirsty throats. 

The existing water bodies such as lakes in the cities are not maintained well. The water bodies are getting polluted due to:

• Garbage is thrown,
• Construction debris is dumped
• Raw sewage is disposed
• Encroachment around the areas  

If we have to tackle this increasing water scarcity, we need to find out a sustainable solution.

How to tackle scarcity of water in urban areas?

a) Unsustainable solutions adopted by Government so far 

The local governments of cities and towns try to tackle the water shortage in the area by:

a) Identifying new and deeper sources of aquifers 

b) Drilling more borewells and tubewells

c) Supplying water through tankers and pipelines brought from distant sources  

d) Setting up desalination units in cities near ocean

All these solutions are temporary, expensive, unsustainable and inviable in the long run.

b) Sustainable solution - Rainwater Harvesting with Artificial Recharge

The need of the hour is to replenish the ground water resources and increase the water holding capacity of the existing water bodies. Thus the viable and sustainable solution to the water scarcity problem in the urban areas would be Rainwater Harvesting in combination with Artificial Recharge of groundwater aquifers.

The rainwater collected from the rooftops of the buildings and stored, can be used either directly or after a preliminary treatment (screening). It can easily meet the demand of an individual household in the water scarce regions. But major problem with rainwater harvesting is the cost associated with creating and maintenance of storage tanks.

To overcome the problems associated with the storage tanks, we can adopt Artificial Recharge technique which helps to replenish the groundwater aquifers. In Artificial Recharge method, the rainwater collected from the rooftops or surface run-offs is made to percolate down the soil artificially, thereby increasing the groundwater levels which recharges aquifers and help to increase water table. 

Which is better - roof catchment or ground catchment and why?

The roof catchment is better that ground catchment as the rainwater collected from the well maintained roofs prevent the water from getting polluted whereas in ground catchment, the surface run-offs can get polluted as it picks up litter, debris, chemicals, sewage and other toxic substances, whatever comes in its way.

What are the issues with Rainwater Harvesting systems? 

The main problems associated with adoption of Rainwater Harvesting systems are:

1) Economics and Technology

The total cost of installing rainwater harvesting system is high.

a) The major cost is associated with building a storage tank and maintaining it.

b) Around 20% cost of installing rainwater harvesting system involves installing collection gutters, downpipes and filters.

2) Water Quality and Health

The quality of water collected by rainwater harvesting depends upon following factors:

• User behavior
• System design
• Environmental Conditions

We need to make sure:

a) Storage tanks are maintained dark and sealed

b) There is regular cleaning of storage tanks and roof surfaces

c) The taste of water does not change upon storage

d) The quality of stored water does not deteriorate over time

e) The storage tanks does not become home for diseases vectors such as mosquito larvae. Adequate vector control measures need to be taken.

3) Water Policies, Regulations and Attitudes

Create awareness among the masses about the advantages of using rainwater harvesting systems.

Artificial Recharge by utilizing harvested rainwater

The groundwater aquifers are replenished naturally by percolation of surface run-offs, stream flows or melting snows in the ground. Artificial Recharge is a technique where water is introduced in the groundwater aquifers by artificial means in lower costs.

Artificial Recharge reduces concentration of pollutants in the water which percolates down the soil through dilution effects. The biggest advantage of artificial recharge over storage structures of rainwater harvesting systems is that there is no additional cost required to maintain and operate the storage tanks over time as all the harvested water directly reaches the aquifers without requiring storage.

Artificial recharge can be done by two methods:

a) Surface spreading technique

b) Injection wells  

The surface spreading technique is used when the top surface of aquifer is highly permeable with high infiltration rate. The types of surface spreading techniques are:

1) Dams and weirs are constructed on flowing streams and rivers 

2) Canals and channels are build over permeable surface of aquifer

3) Recharge through basins/pits/ponds and trenches

A depression is created in the ground and an embankment (eg. of stones) is created to hold water. The water is allowed to percolate down the soil to the aquifer.

The injection technique is used when the top surface of aquifer is less permeable with low infiltration rate. The perforated section of the well or bore helps the water to infiltrate down to aquifers.

• Abandoned wells/bore or hand pumps can be used to recharge aquifers

Benefits of Rainwater Harvesting and Artificial Recharge in Urban areas:

1) Storm water management by reducing surface run-offs

2) Increase in water table and replenishment of groundwater aquifers

3) Improvement in groundwater quality

4) Reduce dependency on Municipality to supply water 

Continue to read about:

What is RAINWATER HARVESTING? Catch the water where it falls

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