Tuesday, February 28, 2023

SV Symphony apartments - A case study of direct borewell recharge using filtered rainwater

SV Symphony is an apartment complex in Janatha colony in Carmelaram. It consists of 52 flats and occupies an area of about 0.5 acres. The complex consists of 2 and 3 BHK apartments. The lay of the land within the premises slopes slightly from north to south. The children’s play area on the southern side is the lowest point of the land.

The entrance to the apartment complex is into the car parking area which is about 4 feet below the road level.

Fig 1: SV Symphony apartment (left: location on the map; right: Satellite view of the apartment)

1.0 Summary
SV Symphony apartment complex had been facing water scarcity since its inception. They do not have a BWSSB Cauvery connection and were heavily dependent on tanker water which was very expensive. The proactive owners however tried to ease their water woes by implementing rooftop rainwater harvesting and direct borewell recharge. This has resulted in the complex consuming less tanker water while increasing its borewell yield thereby aiding its water security.

This case study looks at how these interventions were undertaken and their effects on the water sustainability of the apartment complex.

2.0 Background
The only source of water in the apartment complex is borewells. Three borewells were drilled during its construction, but these did not meet the apartment’s needs. Due to this, they have always been heavily dependent on tanker water which costs around 13 to 14 lakhs per annum.

Fig 2: SV symphony apartment complex

Early on, the residents of the apartment complex were on the lookout for better water management solutions. One such well-informed resident was Mr Samir Rakshit, who was an ardent proponent of water conservation. After some research, he and a group of residents contacted Mr Ayyappa Masagi to help solve their problem. Direct borewell recharge with filtered rooftop rainwater was suggested.
As in many communities, this community too faced some initial resistance to this initiative. But after some discussions on technicalities and budgeting, the complex was convinced to take the initiative forward.
A few amenities were still under construction at this time. Hence, after some discussions with the builder, the flat owners managed to get involved with the design and implementation of their rooftop rainwater harvesting system.
Samir believes that the size of the community was a big factor in the success of this initiative. In his words, “We were lucky to have a smaller community at the start. Moreover, since we started this early on and much before the apartment was fully occupied, the pushback was also manageable.”

3.0 Sources of Water

3.1 Borewells
During the construction in 2014, the builder drilled three borewells, each 1100 feet deep. Out of these, two borewells (borewell 1 - near the pool and borewell 2- in the children’s play area) did not yield any water. The third borewell (borewell 3- near the exit gate) was the only one that yielded some water. But this was not enough to meet the apartment’s needs. The location of all these borewells is depicted in figure 3. Since there are no meters to the borewells the exact yield is unknown.



Status after digging

Borewell 1

Near pool

Zero yield

Borewell 2

Near children’s play area

Zero yield

Borewell 3

Near exit gate

Average yield

Table 1: Status of all three borewells (depth: 1100 feet)

3.2 Tankers
The apartment heavily relied on tanker water throughout the year. About 40 to 50 tankers of 13 KL capacity were purchased every month. This cost around ₹70,000 per month (₹1400 per tanker). The total amount spent on tanker water per month and year is shown below.

No. of tankers/ month

Capacity per tanker (KL)

Cost per tanker (₹)

Tanker water consumed/annum (KL)

Cost of tanker water/annum (₹)





8.4 L

Table 2: Tanker water consumption and its cost per annum

4.0 Water Storage

Two underground sumps of 16 KL each are present near borewell 3 and are connected internally. Borewell and tanker water are mixed and stored in these tanks.
Water from here is then pumped to three 4 KL overhead tanks (total 12 KL capacity), which are then supplied to the houses directly.

Fig 3: Three 4KL overhead tanks

Another sump for storing rooftop rainwater was initially constructed on the eastern side behind the second lift. This location was however inconvenient for the system and hence is currently dysfunctional. The apartment complex does not plan to use this sump in the future either.

5.0 Water demand
Assuming a family of four in each of the 152 flats and an average daily consumption of 135 litres/person/day, the annual water demand for one flat is as in the table below.

No. of people/flat

Consumption/person/day (L)

Total consumption per day (L)

Total consumption per annum (KL)





Table 3: Annual consumption for one flat

From the table above, the approximate water demand for all 52 flats is approximately 10244 KL/annum. Of this, only around 2444 KL/annum of water demand was being met by the borewell, and 7800 KL/annum of taker water was required to bridge the gap.

6.0 Rooftop rainwater harvesting

To increase the yield of the existing borewells, direct borewell recharge with rooftop rainwater was undertaken. To set up this system, the rooftop was divided into two parts – one section with a catchment area of 15500 sqft (1440 sqm), and another of 1440 sqft (134 sqm). This is depicted in Fig 4 below.

Fig 4: Rainwater harvesting plan in SV Symphony (Pic credit: Citizen Matters)

6.1 Rainwater harvesting potential
Calculating rainwater harvesting potential is a method of estimating how much rainwater can be harvested from rooftops by assuming that 90% of rooftop runoff can be harvested.
The rainwater harvesting potential for the two parts of the rooftop with average annual rainfall and mild rainfall is given in the table below.

Part of rooftop catchment

Area (sqm)

Runoff coefficient

Annual runoff at 974.5 mm rainfall (KL)

Runoff at 30 mm rainfall (KL)

North part (water stored and used)





South part (water not stored)









Table 4: RWH potential

As seen in table 3, the maximum rainwater that can be harvested per annum by the apartment is 1440 KL. This shows that harvested rooftop rainwater can meet 4.8% of the water demand of 10244 KL.

6.2 Storage and Recharge of Borewell 3
The only functioning borewell was borewell 3, which was picked first for intervention. Rainwater from the northern part of the rooftop which is 1440 sqm (~91% of the rooftop area) is channelled into a masonry filter. Filtered water is then directed into the two sumps (of 16KL capacity each) that are located near this borewell.
Overflow from these sumps is led to the borewell where direct borewell recharge has been implemented. The stored water from the sumps is pumped up to the three overhead tanks and then supplied to the flats directly.


Volume of water (KL)

Rainwater that can be harvested from 1440 sqm area (for 974.5 mm rainfall)


Total storage capacity (sump+overhead tanks)


Volume of water used for direct borewell recharge


Table 5: Volume of water stored and used for recharge

Fig 5: Left: Masonry filter for RRWH; Right: Borewell with direct recharge

6.3 Recharge of Borewell 2
In 2021, the second borewell located in the children’s play area was similarly recharged with rainwater falling on the southern section of the rooftop, of 1440 sq ft area (134 sqm). Unlike the northern part, this water is not stored in a sump. All of this water is used to recharge borewell 2 after passing through an on-site filter at the borewell. Though the yield of this borewell has increased, it is not used much, as the first borewell suffices for their needs.


Fig 6: Borewell 2 in the children’s play area

6.4 Total savings on tanker water purchase
Efforts towards rooftop rainwater harvesting and direct borewell recharge have led to a considerable reduction in tanker water consumption at the apartment complex. As mentioned earlier, around 40-50 tankers were being purchased initially every month even during monsoons. After interventions, this has been reduced to about 25 tankers per month for about 5-6 months of the year only. There is no tanker water consumption during the monsoon season. The following table captures these numbers.

Before intervention

After intervention

No. of tankers per month 

40-50 per month for 12 months

20-25 per month for 5-7 months

Volume of tanker water consumed/year (KL) - 13 KL/tanker



Cost per year (₹) - ₹1400/tanker



Table 6: Cost of tanker water before and after intervention

From the above table, it can be seen tanker water consumption has reduced by 5525KL/annum which is a saving of about ₹2,45,000/annum.

6.5 Concerns about water quality
Some flat owners expressed some concerns about the quality of harvested rainwater that was recharging the borewell. Though a formal lab test was not conducted Samir and team periodically monitor the output water by sight and smell and circulate the photos through Whatsapp and email.

6.6 Efforts to keep the rooftop clean
Every rooftop rainwater harvesting system requires the rooftop to be kept as clean as possible. Restricting footfall on the rooftop is the most common strategy that is employed in most apartment complexes for this purpose. However, there was a major backlash to this suggestion by the residents. Hence, a compromise was made to allow some basic tasks like clothes drying etc. The housekeeping is however vigilant in keeping this area clean. Instructions have also been printed and published at the entrance of the rooftop for the same and footwear is not allowed in the terrace area.

6.7 Savings and water security
The apartment has spent ₹1.6 lakhs for the implementation of this system. But Mr Samir claims that they have used 14 million litres of pure rainwater in the last five years. This would cost approximately 14 lakhs. Hence, they have been saving around ₹3 lakhs per year.
There is also the added advantage of water security due to these efforts.

6.8 Future Plans
During heavy rains the rainwater that is channelled into borewell 2 tends to overflow. Due to this, it was decided to try and use this water to recharge the borewell that never yielded any water (Borewell 1).
The apartment still ends up buying around 150-175 tankers of water per year, much of it in June - during the peak of the dry season. However, their tanker water use has reduced considerably.
The apartment complex plans to build more overhead tanks to increase its water storage capacity leading to a further reduction in its dependency on external tankers.

7.0 Sewage Treatment Plant (STP)
The STP that the builder had installed had become dysfunctional soon after the handover. The apartment was sending out untreated water into the sewage line for a while. But a sum of ₹2 lakhs was soon collected from the flat owners to restore its functionality.
This STP occupies an area of about 75-80 sqft of space. The treated water is stored in a 5 KL overhead tank. The STP is placed between the entry and the exit gate as shown in fig 7.
The treated wastewater is reused in the flush tanks of all the flats. There is, however, no space for a garden area in this apartment complex and hence the unused treated water is currently sent out of the apartment.

Treated wastewater demand for Flushing

Flushing requirement per person (litres)/day

No. of people per flat

Total water required for flushing for 1 flat (litres/day)

Total water required for flushing for 52 flats (litres/day)





Table 7: Treated wastewater demand

Assuming that about 80% of the water consumed by the apartment is being discharged as wastewater and treated, the volume of treated water generated is 8195 KL/annum. From the above table, 3036.8 KL/annum is required for flushing in the apartment.

Fig 7: STP between the gates

8.0 Water demand management

8.1 Pool closure
The builder had handed over a moderate-sized swimming pool to the residents of the apartment. The pool needed 13 KL of water every day. One whole tanker was used to fill in the pool per day. However, after facing severe water scarcity from 2016 through 2018, the apartment complex decided to close this pool completely so as not to waste water. This was undertaken after a poll was conducted with the owners of the apartment. There are also plans to reuse the tank of the pool for storage purposes.

Fig 8: Closed pool

8.2 Aerators and other water-saving attachments
Aerators for all taps have been mandated in all houses. Some enthusiastic owners have also installed other water-saving fixtures like water-saving shower heads etc.
Metering has however not been implemented here due to the complex plumbing system employed by the builder.
There is widespread awareness of sustainability among the residents of this apartment complex. Continuous monitoring, follow-up and education are carried out.

9.0 Media Coverage

In September 2019, when many of the apartments in the area were hit by a drought-like situation, this apartment was unaffected due to their efforts towards rainwater harvesting. This was covered by the journal Citizen Matters and is linked here:

10.0 Conclusion
SV Symphony apartment was built and handed over to the owners at the end of 2015. However, with the efforts of flat owners who had moved in early, the rainwater harvesting system was in place by March 2015. This apartment has demonstrated the benefits of the cooperative efforts of the builder and residents to achieve water security in the apartment complex through rooftop rainwater harvesting and direct borewell recharge.

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