What is in Urban Water Management

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Rainwater harvesting (RWH) has evolved as a model to conserve water and also to effectively discharge used water back into the ground; thereby recharging the water tables and keeping them accessible. Urban environmentalist Indukanth Ragade from Chennai and Shubha Ramachandran, Water Sustainability Consultant with Biome Environmental Trust, Bangalore, share the total perspective on RWH with the systems and models in use in Chennai and Bangalore respectively, with Vijayalakshmi Sridhar.

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In the olden days, with the ground well being the sole water source and recharge point, a cyclic movement of water within the plot is initiated so that rainwater is harvested and used water is redirected into the ground or well. Therefore, each household was self-sufficient in its water requirement and usage. The same model was applied across villages, panchayats and towns keeping them well supplied throughout the wet and dry seasons.

However, with increasing population, migration to cities, modern town planning and the municipal water supply cut the dependence on wells. Resultantly, the household used water flowed into the central sewerage system. Since there was no movement of water back to the soil or the water source, the wells dried up and water tables sunk deeper. Sadly, the demand has multiplied and now is the time for us to revisit the old methods.

“The only way to avoid a consequent urban water crisis is to try and revive the earlier circular movement of water as much as possible,” says Indukanth Ragade. Ragade’s comprehensive system involves harvesting each drop of water that falls within a residential premise and diverting it to a single source, possibly to a well. This includes the rainwater from the terrace through pipelines, the water falling on the open spaces around the building and the water that falls on the paved driveways of apartment complexes that gets cleaned as it passes through the ground. In some projects, Ragade has worked to divert the terrace water to a sump and the overflow from the sump to the well. “The shallow dug wells provided in more than 150 four-storeyed complexes, built by the company of which I was a part of, are serving the residents well as they are sustained by all the rainwater falling in the premises,” Ragade cites proof to his point.

In Shubha Ramachandran’s view, rainwater harvesting has to be seen in a case to case basis for it to be a viable solution to meet the regular and rising demand for water. “At the household level, trapping and using all the rainwater that falls on the plot, brings in a kind of water autonomy. In fact, coupled with some other measures, it can give 100 per cent autonomy.”

Bangalore’s dependence on wells stopped when the communities switched to the Cauvery water supply. The city gets about 970mm of rain every year, and 70-80 thousand litres of rainwater and household harvesting can see through the water demand for a family of four for about four months on the assumption that the consumption is 600 litres per day (135 litres per capita per day).

Ramachandran explains how ground wells can be used as a reliable source for large scale RWH. “On a city scale, in a large plot of several acres, recharge wells can be dug and this can improve the water quality in the locality and bring up the water tables too.”

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Water scarcity could be curtailed by establishing a good water economy by allocating more accountability to usage, such as metering individual and community usage and also substantiating these measures with the available stock of water.

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RWH as a state policy

Both TamilNadu and Bangalore have mandated RWH as part of the State’s policy. Repeated spells of scarcity or the fear of facing it have urged the people to invest in RWH systems. The awareness and the willingness among the public, the service and service providers are high in Chennai and Bangalore compared to other cities.

The TamilNadu Government’s RWH mandate issued in 2003 included only the terrace harvesting and grey water treatment compulsory. But harvesting the run offs in the premises and recycling were not part of the mandate. However, the awareness among the public has helped the expansion of the concept and the system. “In places where the dug well was not feasible for any reason, the borewells were charged with rainwater by providing a pit stabilized with RCC rings around them, replacing the borewell pipe with a slotted pipe, covering it with nylon mesh and directing the rainwater into the pit,” says Ragade. Though this was not as efficient as a dug well, it proved to be an efficient alternative.

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A three-compartment overhead tank, instead of the conventional two-compartment tank, can be installed. This enables more effective use of available water of different qualities that can be stored separately and the better quality used for bathing and the worse quality for flushing.

– Indukanth Ragade

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For Bangalore, the key lies in achieving a greater scale of sustainability, for which proper management is considered crucial. “Groundwater and shallow groundwater have to be managed better,” says Ramachandran.

To do that well, and to minimize the load on the public sewage system and the dependence on the municipal supply, there should also be a continuous process of recycling. Water used for bathing and washing (55-65% of usage) should be diverted to a plant bed (Ragade recommends Cannas or Hidechium or Heliconium of banana). The water that runs to the soil gets cleaned and reaches the well.

“In big complexes, water can also be physically collected and reused for flushing of closets which constitutes 35% of total usage. This system operates practically on its own and requires very limited maintenance efforts. The treated water has been tested by the Chennai Metropolitan Water Supply and Sewerage Board several times and found free of all organics. Places which get an average rainfall of 125cm per annum, this method combined with greywater recycling can give almost 70-80% self-reliance or even more,” Ragade assures. “A three-compartment overhead tank instead of the conventional twocompartment tank can be installed. This enables more effective use of available water of different qualities that can be stored separately and the better quality used for bathing and the worse quality for flushing.”

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On a city scale, in a large plot of several acres, recharge wells can be dug and this can improve the water quality in the locality and bring up the water tables too.
– Shubha Ramachandran

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Building concentration is higher in the most developed parts of Bangalore. Though these areas are currently doing well with the Cauvery supply, groundwater recharge should be done in addition to roof top harvesting to augment water availability. Private premises should trap their rainwater and the storm water drains should be tweaked only to hold the road rainwater run off so that they can be a way to put a lot of water into the ground. As an alternative¸ low maintenance open storm water drains or Chapdis can be installed. At a community level, wells can be dug.

For smart cities and newer cities that are being planned, Ramachandran gives us a five point water integration and management plan. “How rainwater can be harvested and used as a viable source, demand management, understanding groundwater, used water recycling and maintenance of water bodies are critical elements,” she says.

Looking ahead

Wastewater is going to be the most reliable source of water in the future for usage. Adoption of appropriate treatment technology at a local level and maintenance of water bodies are important.

Ragade points out the loose ends in the system. “There should be proper dissemination of tried and tested methods. In a survey done two years ago, we found that many of the RWH systems installed in Chennai in 2003 (when people hardly got hardly a month for installation) were non-functional,” says Ragade. “Maintenance of the established systems is crucial for smooth reliance,” opines Ramachandran.

Ragade shares suggestions to improve urban water management. “There should be greater commitment from the Government in RWH and recycling. Most Government buildings themselves do not have RWH systems. Recycling of greywater should be promoted. The CMWSSB (water athuorities in Chennai) have tested my method and found it works. The cost of installing the systems will be negligible compared to the total project cost, if planned and executed during the construction stage itself. This system is also applicable in Smart Cities.

“The government has to look at RWH as a mechanism – a micro water shed that is sustainable in each neighborhood can be established and a measurement of demand and how it plugs into the supply should be undertaken,” Ramachandran concludes.