Rainwater harvesting is the collection and storage of rainwater for reuse on-site, rather than allowing it to run off. These stored waters are used for various purposes such as gardening, irrigation etc. Various methods of rainwater harvesting are described in this section.

Surface runoff harvesting: In urban area rainwater flows away as surface runoff. This runoff could be caught and used for recharging aquifers by adopting appropriate methods.

Rooftop rainwater harvesting: It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is less expensive and very effective and if implemented properly helps in augmenting the groundwater level of the area.

Methods of Rooftop Rainwater Harvesting: Various methods of using roof top rainwater harvesting are illustrated in this section.

Storage of Direct Use: In this method rainwater collected from the roof of the building is diverted to a storage tank. The storage tank has to be designed according to the water requirements, rainfall and catchment availability. Each drainpipe should have mesh filter at mouth and first flush device followed by filtration system before connecting to the storage tank. It is advisable that each tank should have excess water over flow system. Excess water could be diverted to recharge system. Water from storage tank can be used for secondary purposes such as washing and gardening etc. This is the most cost effective way of rainwater harvesting. The main advantage of collecting and using the rainwater during rainy season is not only to save water from conventional sources, but also to save energy incurred on transportation and distribution of water at the doorstep. This also conserves groundwater, if it is being extracted to meet the demand when rains are on. 

Recharging groundwater aquifers: Groundwater aquifers can be recharged by various kinds of structures to ensure percolation of rainwater in the ground instead of draining away from the surface. Commonly used recharging methods are:- Recharging of bore wells, Recharging of dug wells. Recharge pits, Recharge Trenches, Soakaways or Recharge Shafts, Percolation Tanks.

Rainwater harvesting is the storing of rainwater during the monsoon season for the purpose of using it during periods of water scarcity. Generally speaking, it is a process used for collecting and storing rainwater for human use. Rainwater harvesting is best described as the technique by which rain water is accumulated and stored with the intention of reusing it during the dry season or when there is a drought.

Bangalore has the distinction of being the only city with over 300 major lakes in its agglomeration limits. Situated 920 meters above sea level. Bangalore is blessed with a healthy weather. With its beautiful parks and tree canopied roads Bangalore is also well-known as the Garden City. The naturally undulating terrain of Bangalore city, with its hills and valleys forms a unique “radial drainage patterns” which is ideal for capturing and storing rainwater. Each valley at the ridge top gives birth to small streams that cascade down to form major stream systems in the three Valleys of Hebbal, Koramangala Challanghtta and Vrishabhavati.

Over the years increase in the urban population of Bangalore has led to a spurt in the growth of residential buildings, replacing traditional bungalows with their large open spaces. With the demands for land use in developed areas going up many folds vertical growth was inevitable. This has resulted in increase in rooftop areas, pavements and roads. With massive concreting and asphalting of ground areas, the soil exposed for rainwater infiltration has decreased, leading to a drastic fall in the groundwater table and disappearance of open wells. In the last 30 years, Bangalore has experienced five years of severe drought and three years of moderate drought. The quest for water has resulted in over exploitation of groundwater. On an average the groundwater level has progressively declined by 10 meters between 1978 and 2003. Consequently, the quantity of run off water in the storm drains has increased tremendously. Rainwater Harvesting is all about conserving this water, thereby, supplementing the presents supply.

Bangalore City mainly depending on the Cauvery and Bore well water. If the state receives good rainfall then Bangalore city will get the water from the Cauvery otherwise we need to depend on the local lakes, tube wells and underground water. The recharge of underground water is the main challenge in cities like Bangalore. Because many part of the city is covered by the built-up areas. Recharging of rain water in these places will becoming headache for the administration.

Generally groundwater in shallow wells is polluted. Groundwater levels are falling due to heavy extraction and the absence of rechargeable aquifers. In fact, several deep bore wells have run dry. To address the issue of water shortage. Rainwater Harvesting is a perfect solution because Bangalore is ideally suited:

Rainwater Harvesting is a simple, technically feasible and economically affordable option. Its benefits to the individuals institutions and the society are many.

Rainwater Harvesting is a community based programme and its success largely depends on the collective participation of Government bodies NGOs, builders architects, house owners and individuals.

Table 1

Annual Rainfall		Annual Rainwater Potential (in Liters)
		Plot sizes in Sq. feet
in inch	in mm	600 (20’ x 30’)	1200 (30’ x 40’)	2400 (40’ x 60’)	4000 (50’ x 80’)
19.69 31.50 39.37 47.24 55.12 157.48	500 800 1000 1200 1400 4000	28,000 44,800 56,000 67,200 78,400 2,24,000	55,500 88,800 1,11,000 1,33,200 1,55,400 4,44,000	1,11,500 1,78,400 2,23,000 2,67,600 3,12,200 8,92,000	1,86,000 2,97,600 3,72,000 4,46,400 5,20,800 14,88,000

Source: BWSSB data unit.

The above table shows the rainwater potential in Bangalore city based on available rainfall in the place against to the Plot sizes of the same areas.

Advantages of rainwater harvesting: RWH is a quick solution, to increase the availability of water, in areas that have inadequate resources. It increases ground water levels and mitigates the effects of drought. It reduces rain water run-off, which may otherwise, flood storm water drains. It serves as a cost-effective method to reduce soil erosion. However, its successful implementation, depends on the collective efforts of individuals, government bodies and builders. One can store rain water in tanks and use it to flush toilets, water plants, etc. Rain water can also be harvested, to recharge groundwater through recharge pits, dug wells, bore wells, soak pits and recharge trenches.

According to survey held in the year 2018 Reasons for not installing RWH: structures Approximately 18 percent of the respondents have cited four major reasons for not installing RWH structures, such as (1) not being aware of it (2) nobody insisted on it (3) financial problems and (4) lack of space for installing it. Among the people who were not aware of RWH, around 12 percent respondents felt that it was of no use and a waste of money. More than half of the respondents (53.3 percent) cited their advanced age, poor health and the lack of capable persons in the household to carry out the task as reasons for not adopting RWH. It is ascertained that most of these households belong to retired/aged people and their children stay elsewhere. About 16 percent of the families were found reluctant to express their views regarding the non-installation of RWH structures. The below table shows the Rain water Harvesting connections in BBMP region for the last 20 years.

Rainwater Harvesting is a community-based programme and its success largely depends on the collective participation of Government bodies, NGOs, builder’s architects, house owners and individuals. Table-5.2. shows the number of connections in rainwater harvesting annually from 2001-02 to 2017-18 in Bangalore urban. The highest rainwater harvesting connection took place in 2017-18 (25229 connections) followed by 2001-02 (20,081 connections), 2009-10 (18,207 connections), 2011-12 (16,846 connections) and least connections took place in 2005-06 (08 connections), 2007-08 (832 connections). Annually there is variation in rainwater harvesting connection because of individual interest and efforts of Government bodies, NGOs, electronic officers etc., to give proper information’s and awareness programmes regarding importance of Rain Water Harvesting.

As we mentioned earlier there are many reasons why peoples are not interested in RWH. But government has to take some initiatives and popularize the RWH programmes in the Bangalore city.

Bangalore Water Supply and Sewerage Board (BWSSB) is the premier governmental agency responsible for sewage disposal and water supply to the city of Bangalore. The BWSSB was constituted under the act of the Karnataka state legislature and the board came into existence on October 2, 1964. The BWSSB Act 1964 & BWSS rules 1964 amended from time to time. The BWSSB has recently introduced an amendment to its Act and has made rainwater harvesting mandatory for certain sites.

The Bangalore Water Supply and Sewerage (Amendment) Act, 2009, 72A-Obligation to provide rain water harvesting structure states that “Within nine months from the date of commencement of the Bangalore Water Supply and Sewerage (Amendment) Act, 2009 every owner or occupier of a building having a sital area of 2400 square feet and above or every owner who propose to construct a building on a sital area of 1200 square feet and above shall provide for rain water harvesting structure in such manner, with such conditions as may be provided in the regulations, failing which the Board may cause such rain water harvesting structure and recover the cost from the owner or occupier, as the case may be, arrears of land revenue.”

Non-compliance: what if I have not implemented rainwater harvesting? If you have a BWSSB connection and your property falls under any of the regulations and have not yet implemented rainwater harvesting, the BWSSB can impose a levy of additional water supply and sewerage charges as per the BWSSB Amendment to Regulations (2015).

Penalties introduced for residential and non-residential defaulters (BWSSB Amendment to Regulations 2015) - Residential buildings: additional charges of 25% of total water and sanitary charges will be levied for first 3 months and thereafter 50% of total water and sanitary charges till the RWH is provided. Non-residential buildings: additional charges of 50% of total water and sanitary charges for first 3 months and thereafter additional charges of 100% of total water and sanitary charges till the RWH is provided.