Detailed case study of water sustainability measures undertaken at Nandi Deepa apartments

1. Water sustainability: The story of Nandi Deepa Apartment
1. Introduction
Nandi Deepa is an apartment complex located on Bannerghatta Road in south Bengaluru. It
was constructed by Nandi Builders in 2005 and contains six blocks and 160 flats. About 350
to 450 residents currently occupy about 109 flats. This complex has an STP (Sewage
Treatment Plant) and uses the treated wastewater for flushing toilets and gardening. In
addition to this, it requires between 48,000 to 50,000 litres of fresh water per day.
Nandi Deepa Apts - pic and location
2. Context
BWSSB (Bangalore Water Supply and Sewerage Board) supplies water from the Cauvery
River to parts of Bengaluru. However, this apartment complex doesn't receive Cauvery
water and has had to face acute water shortages for nearly a decade. Initially, the residents
relied on water from borewells within the complex. But this was not enough. So, they began
to buy tanker water. Over the years, the yield from the borewells kept decreasing. In 2016,
the situation reached a crisis point as the borewells ran dry. From then on, the residents
depended entirely on water tankers. For this, they spent Rs 14 to 16 lakh annually.
The water situation improved after a new Residents’ Welfare Association (RWA) was formed
in June 2020. The newly elected members came up with an action plan for sustainable water
supply. They decided to revive the existing open well and borewells, and implement
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2. rainwater harvesting and groundwater recharging. This would reduce their reliance on water
tankers and cut down their annual costs. Recorded below are the details of the successful
implementation of this water management plan.
3. Sources of water
3.1 Borewells
There are four borewells within the apartment complex.
Borewell No. Year of drilling Depth (feet) Stopped yielding from
1 2009-10 850 Still yielding
2 2001-02 350 2013
3 2001-02 400 2016
4 2001-02 450 2009
Borewell nos. 2 to 4 were drilled by the builder. The water in borewell no. 2 was full of silt.
So, no motor was attached.
Initially, borewell no. 4 yielded enough water, and residents were largely dependent on it.
However, the yield began to decline in 2009. So they drilled a new borewell, almost twice as
deep as the others - borewell no.1. They relied on this new borewell until 2016, after which
its yield declined as well.
3.2 Water tankers
After 2016, residents depended entirely on water tankers.
Capacity of each water tanker 4200 litres
Cost of each tanker Rs. 320
Number of tankers needed per day 14 to 16
Total cost of water tankers per year Rs.14 to 15 lakhs
Annual water tariff paid by each household Rs. 7,000
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3. 3.3 Cauvery Water Supply
To receive a BWSSB Cauvery water connection, the previous association had paid an
advance of Rs 5 lakhs. A balance of Rs 15 lakhs is yet to be paid. Cauvery water connection
was expected to have been given in 2020, but it has been delayed.
3.4 Open well
The land on which the apartment complex was built on was once a coconut grove. The trees
were irrigated using water from an open well, which is more than 100 years old. It is said that
the well never went dry, though the water level decreased in summer. Both the diameter
and the depth of the well are 20 feet.
This open well still exists in the complex. The builder had covered it with a concrete slab, and
residents used it for car parking. The new residents’ association decided to rejuvenate and
use this well to help deal with the water crisis. When they uncovered it, they found the
water level in the well was 15 ft.
4. Storage infrastructure
This apartment complex has a diverse water storage infrastructure.
Type of storage Capacity per
container
(litres)
Total
no.
No. in
use
Total
capacity
used
Remarks
Sintex® tank
(underground)
5,500 12 5 27,500 5 tanks are cracked, 2 are
kept aside for spare use
RCC sump type 1 40,000 3 2 80,000 Kept aside for spare use
RCC sump type 2 20,000 3 3 60,000 These are to replace the
damaged Sintex tanks
OHT (Over Head
Tank)
16,500 16 16 264,000
5. Treatment infrastructure
5.1 Water Treatment Plant (WTP)
The association wanted to check the quality of the open well water before using it. A water
quality test showed high turbidity. So, a Water Treatment Plant (WTP) was set up.
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4. The WTP was designed and implemented by Pune-based vendor NMJAL Maitreya. It was
installed in 2020 for Rs 8.85 lakhs. It follows a process of Activated Filter Media, Activated
Carbon Filter and Chlorine Dosage System. It can treat 5000 litres an hour.
Water is first pumped from the borewells into a 40,000 litre sump, using a 1.5 HP (Horse
Power) motor. It is then sent through the WTP. After treatment, the water is pumped into
three 20,000-litre sumps. Water from the open well is also treated in the WTP and pumped
to a 40,000-litre sump.
5.2 Sewage Treatment Plant (STP)
There is an STP with a capacity of 1.1 lakh litres installed by the builder. It uses the Extended
Aeration Activated Sludge Process. Treated wastewater (TWW) from the STP is used for
gardening and flushing toilets. Gardening requires between 15,000 to 20,000 litres a day,
and flushing toilets requires about 35,000 litres a day. The treated wastewater is used
efficiently, and there is no excess.
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5. 6. Water management plan
6.1 Creating a team
The new residents’ association was formed in June 2020. It consisted of 6 members. They
audited the annual expenses of the apartment complex and found that a significant portion
of their spending was on water. So they decided to reduce this spending. Mr Joe Christopher
was appointed as the joint secretary and took over the responsibility of water management.
He put together a group of 7 interested residents, aptly called the Water Team.
They first explored the option of getting a BWSSB Cauvery water connection. As mentioned
above, a Rs 5 lakh advance had been paid, and an additional payment of Rs 15 lakh was
pending. Mr Christopher went to the BWSSB office at Cauvery Bhavan. He found out that
apartment complexes with more than 20 flats could only get a Cauvery water connection if
they met the following 3 requirements:
● Individual household water metering
● Auto overflow controller for the overhead tank and sump
● Implementation of rainwater harvesting
They decided to implement the 3 requirements specified by the BWSSB. For rainwater
harvesting, they found that when it rained, a lot of runoff water was generated within the
apartment complex. They had to figure out how to store and use this water. The team
brainstormed many ideas, such as - building a sump of 1 lakh litre capacity, using stormwater
to recharge groundwater, directing water from the rooftop into the open well, using the
open well, creating a sloped structure to hold water, etc.
Finally, they decided to revive both the borewells and the open well.
6.2 Reviving borewells through recharge wells
6.2.1 Inspecting the borewells:
By 2016, the borewells had gone dry and were left unused. In 2020, the team decided to do a
camera inspection to check the current water levels. It showed there was some water in the
borewells again. Details of the inspection report are in the table below.
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6. 6.2.2 Using the borewells again:
Based on the inspection report, the association decided to attach motors to all the
borewells and start using them, except no. 2, which had silty water. Details of these changes
and the cost savings are listed in the table below.
Details of borewell usage and savings on expenditure (28 November 2020)
BW
No.
Used since Hours of
use per
day
Amount spent
on borewell
revival
Reduction in
no. of water
tankers
Cost
savings per
day
Cost
savings for
30 days
1 22/08/2020 5.5 Rs 41,000 2 (13 to 11) Rs 640 Rs 19,200
2 29/08/2020 5.5 Rs 29,220 1 (11 to 10) Rs 320 Rs 9600
3 10/08/2020 3 Rs 42,353 3 (10 to 7) Rs 960 Rs 28,800
Total Rs 1,12,573 6 Rs 1,920 Rs 57,600
[Source: Mr Joe Christopher]
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7. The association is also considering using borewell no. 2 and treating the silty water with the
Water Treatment Plant.
6.2.3 Digging of recharge wells:
In December 2020, a circular recharge well was dug around borewell no. 4. Its diameter was
4 ft, and its depth was 20 ft. The recharge well was lined using 25 concrete rings, each of
height 9 to 10 inches, placed one above the other. Between the well wall and the borewell
casing, layers of 40 mm and 20 mm gravel and sand were added to a depth of 1 ft. Holes
were made in the borewell casing.
When it rains, surface runoff water or stormwater enters the recharge well and then flows
into the borewell through the holes in the casing. Silt in the water is filtered by the layers in
between.
[Biome does not recommend direct borewell recharge with surface runoff or stormwater, as it
can contaminate the deep aquifers. Only clean, filtered rooftop runoff should be used for
direct borewell recharge.]
6.2.4 Measuring the impact of the borewells and recharge well:
● After the borewells were revived, the number of water tankers required each day
decreased from 13 to 7, a reduction of almost 50%.
● After the recharge well was dug, the yield of borewell no. 4 was observed to increase
dramatically. (Note: It is not possible to quantify the exact increase as there is no
meter on the borewell and no record of hours of pumping. The meters are at the
sump, which stores water from all the borewells.)
● Due to the recharge well, water in borewell no. 4 increased after a rainy period. After
a dry period, the water level went down again.
Period Rainfall Yield in
borewell no. 4
Number of daily
water tankers
December 2020 to
February 2021
A few showers Went up Decreased from 7 to 3
March and April 2021 Dry Went down Increased from 3 to 7
May 2021 Pre-monsoon
showers
Went up Decreased from 7 to 3
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8. In August 2020, 3 more recharge wells of 4 ft diameter and 20 ft depth were dug to recharge
the surface runoff.
Digging of recharge wells
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9. 6.3 Reviving the open well through rooftop RWH
The association also wanted to use the open well water to reduce their dependence on
water tankers. But there were two issues:
● Water quality: In 2008, the well was once used to store treated wastewater. The well
was cleaned twice after that. However, convincing residents to use the open well
water was still challenging. The association got the water quality tested, and it was
found that turbidity was high. They decided to set up a Water Treatment Plant to
treat the open well water before use.
● Water level: The water level started to go down. The association decided to let
rooftop rainwater flow into the open well. This would increase the water level and
improve the water quality.
Open well during and after cleaning
Clean rooftop water entering the well
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10. The association engaged well-digger Mr Muniraju to rejuvenate the well and redirect
rooftop rainwater into it.
7. Rainwater harvesting potential
Rainwater harvesting potential estimates how much rainwater can be harvested annually
from rooftops and surface runoff, assuming 70% of paved area runoff and 90% of rooftop
runoff can be harvested.
The following table presents the rainwater harvesting potential of Nandi Deepa apartment:
Rainwater harvesting potential
Type of catchment Area (sqm)
Runoff
coefficient
Runoff generated
at 30 mm rainfall
(in KL)
Annual runoff at
974.5 mm rainfall
(in KL)
Rooftop area 4065 0.9 109 3564
Paved area 10099 0.7 212 6889
Rooftop area+paved
area runoffs 14164 322 10454
Nandi Deepa apartment has the potential to harvest 10454 KL of rainwater annually. The
open well alone could recharge 3564 KL of rooftop rainwater annually.
8. Economic feasibility
Initially, residents were reluctant to pay the capital cost of implementing water sustainability
measures. However, Mr Joe Christopher did careful calculations to show that the savings
due to these measures would pay off in a short period. That is, the return on investment
would be high.
Total capital cost Rs 22.2 lakh
Decrease in monthly water costs (from 14 to 7 water tankers) Rs. 62,720
Further decrease in monthly costs (from 7 to 4 water tankers) Rs. 35,840
Potential annual decrease in water costs Rs. 7,52,640 + Rs.
4,30,080 = Rs 11.82 lakh
So, in just two years, they would recover their capital costs.
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11. 8.1 Production cost of water
Production cost of water is a method of arriving at the overall cost of different sources of
water per kilolitre. The following table shows the production cost of water for borewell,
Cauvery and tanker water:
Source of water Cost of water (per KL in Rs)
Borewell 26
Cauvery without sanitation cess 30
Cauvery with sanitation cess 116
Water tankers 76
Open well 10
The above table shows that open well water costs the least, as well as having the lowest
energy footprint.
9. Feedback from residents
Mr Joe Christopher said, "Our society is privileged to have a magnificent open well. We are
happy to revive the open well and use it optimally. We also aimed to have a good RWH
system in our society. We are pleased about the fact that we could reduce the cash outflow
on the water tankers. We are already recovering our capital investment in the form of
investment return. We will be digging three more recharge wells around the other borewells
and planning to install individual household metering very soon.”
10. Next steps
● Using water from borewell no. 2: The association plans to use the silty water from
borewell no. 2 after treating it in the Water Treatment Plant.
● Digging more recharge wells: After seeing the positive impact of direct borewell
recharge at borewell no. 4, they plan to dig recharge wells around each of the other 3
borewells and redirect surface runoff into them. (Please see Biome’s cautionary note
on direct borewell recharge using surface runoff).
● Water metering: They plan to install individual household metering to satisfy the
BWSSB’s Cauvery water connection regulations.
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