Rainwater Harvesting Systems for Existing Properties- Challenges & Cost-Effectiveness

Many states in India have passed the legislation for having a compulsory rainwater harvesting system, being installed in houses or other buildings. In some states, the law is only applicable for new construction, while in some cities like Bangalore, it is made compulsory for all the existing properties as well. There are inherent challenges of installing an RWH system in previously constructed buildings. This blog will enlist all those challenges.

Though the practice of conserving and reusing rainwater in India has been into existence since ages, its real importance is only felt in the past few years. It takes a lot of awareness to gather people for their cooperation in such a benefitting initiative. Making things legally mandatory, helps even more in such scenarios. Hence, the installation of a rainwater harvesting system is now a mandate, for all the newly constructed buildings, in the states of India.

A legislation was passed and by far, 15 states/UTs have adopted the rule including Tamil Nadu, Goa, Andhra Pradesh, Kerala, New Delhi, et al. The legislation applies with immediate effect on the new construction. But what about the existing properties? They have been awarded a certain time frame for taking up this activity. It is because installing a system for harvesting rainwater is not a simple task. They require an extensive planning and a lot of structural changes, to make a premise ready for RWH system.


Challenges faced by existing buildings while installing a rainwater harvesting system

A sophisticated rainwater harvesting system has two basic installable parts – the conduits or pipes and a storage vessel. The third component i.e. a catchment area is generally the roof of the house or a building. While retrofitting these parts in the existing buildings, the old arrangement of pipelines and drains needs to be studied for feasible changes.

Challenge #1: Disruptive aspects and cost

The best practice of rainwater harvesting is to build an underground storage tank, so that stored water can be kept safe from external contamination and weather change. To build an underground storage tank in existing building, a heavy digging will be required. This is a highly disruptive process and requires more maintenance over time. It is undoubtedly a costly and time-consuming affair. The disruption may result in re-routing of some services, to accommodate the installation process.

Challenge #2 Pipework & Plumbing Changes

The other challenge involves the finding of an appropriate location for building RWH structure. Once done, the network of drainage pipes must be considered. One may be able to co-joint the RWH systems pipe with the existing one or you may necessitate re-laying the arrangement. It is again disruptive and involves changing is the levels of some of the pipework. Care must be taken to not to disturb the basic model of the pipe system. The systems included sewer pipes as well. Make sure, the RWH system pipes and sewer pipes have been spaced separately. The complexity of the pipes network is usually high in the older Indian constructions.

Challenge #3 Drainage system’s Issue

While installing a drainage system for supplying water from a rainwater harvesting scheme, care must be taken to ensure that it should only carry water from roof surfaces. It is not uncommon, particularly on older properties, to have a drainage that combines the drainage of ‘grey’ water sources such as baths, basics, etc. and the cleaner water source. In such a scenario, major changes in the drainage system will be on the list.

 A common solution

To avoid disruption to the existing building, an above ground tank, instead of an underground tank, can be designed. It will be easier to construct and maintain them for future repairs and cleaning. However, the above ground tanks can be unsightly, may hamper with the beauty of your premise and occupies a significant space. But if you have a garden or patio, it will be more convenient to have an over-ground storage tank.

 Pre-checks before the installation 

  • If you have decided to install an underground storage tank, then you must ensure that its construction is not impacting the foundations of a building. Follow the thumb rule- tank must be installed twice as far away from the building as the depth of the hole. For instance, if the tank installation hole is 1.5m deep, the tank must be installed 3 metres away from the building.
  • Clarify all construction norms and consultation with your local building control before digging any structure.
  • The size of the bore pipe for pumping the water must be calculated. It is suggested that it the storage tank is installed more than 25 metres away from the building, the bore pipe of 32 mm or larger must be used, instead of the standard 25 mm pipe.
  • Also, in case of installing the storage tank far from the property, the gradient of the drainage pipes must allow water to flow.
  • If the long drainage runs into the tank, it is required to put the tank deep into the ground. As it is not advisable, you would have to consider installing the tank closer to the building to keep the tank shallow.

How to make the installation cost-effective

The exact cost of rainwater harvesting methods depends on the site’s specification. Hence, the generalization of the cost will not of any use.

The cost of building a catchment area is saved though if the system is being installed on the existing building. The pipe connections will take up the major cost. On an average, a typical RWH system would cost between Rs.2,000 to 30,000, for a building of about 300 sq. meter.

You can lower the cost by thoughtfully fixing up the slopes of roofs and location of rainwater outlets. Research and talk to government authorities over the subsidy provision enacted in your state. When the installation is done at a community level, the per capita investment goes down.

Chaitanya Rain Harvest Products and Systems – Your RWH Initiative Partner

If you are taking a part in this noble mission of conserving rainwater to save environment and energy consumption, Chaitanya must be remembered as trusted name-partner for all your concerns.

We are running this blog portal to provide you with every piece of information, concerning rainwater harvesting. We also provide consultation services regarding the pre-installation activities of rainwater harvesting system. This includes site’s inspection, feasibility report, system’s engineering design, system’s layout, hydrogeological survey, and borewell.

We also have products which are a part of rooftop RWH systems such as rooftop drainage gutters, filters.

For recharge structures like borewells, we provide gravels and precast RCC Hume pipes collar rings.


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