The climate of India has nurtured a variety
of traditional systems of water harvesting and supply. The
architecture of water storage, is a lesson in the architecture
of necessity. These systems and structures are fast becoming
the victims of a changed life style, due to available alternatives,
most of which are expensive, impersonal and ecologically irrational.
In Bharuch, a small town in Gujarat, the practice of using
the 'Tanka' an indigenous system of water harvesting and storage
is still practiced by a few Parsi households. Even though
so useful and self-sustaining, this system is fast disappearing.
The neglect of these fine systems and monuments needs attention.
Harvesting water for survival.
Rainfall in India is seasonal, spread over
roughly three months all over the country. The runoff is swift
and heavy. For this reason rainwater harvesting was as common
a practice as the harvesting of the fields for food. The principle
of rainwater harvesting is to collect/store water where it
falls.
The Zoroastrian tenets of 'Asha' proclaim and
celebrate the sacred nature of elements i.e. fire, water,
earth and air. The Zoroastrians treat water not only as a
life giving entity but also a living element. Offerings of
flowers and food is made to water specially on it's 'birthday',
the celebration of the 'Ava parab'.
The Tanka of Bharuch.
In the arid state of Gujarat, water has always
played a very dominant role in the social-cultural life of
people. The step well (vaus) of Ahmedabad and Jodhas of Rajasthan
are well known examples of water storage systems. However
the Tanka, is a much simpler and very personalized system
of water collection and storage. The Zoroastrians are believed
to have brought the concept of harvesting water from ancient
Iran to Bharuch.
All the Tankas are very old structures most
over a 100 years old. The 'Tanka' is an underground tank,
accommodated inside the house, made of chiseled blocks of
stone, in lime mortar. It is made waterproof by an indigenous
herbal mix, which seals minor cracks and prevents bacteriological
growth inside the Tanka.
The size of the Tanka is large enough to store
sufficient drinking water for a family for six to eight months.
An average storing capacity of the Tanka is around 25,000litres.
With sizes reaching nearly20 feet by 60 feet and height of
12 feet, arches and vaults were needed to support the earthwork
and the superstructure on top of the Tanka.
When required to be cleaned, Tankas must be
emptied manually, they are large enough for people to enter
and work inside. The Tanka floor slopes into a sump right
under the point from where the water is drawn out.
The Tanka feeds on the rainwater collected through
roof runoff. A simple system of collection, via a 3" to 4"
pipe, depends on successive sumps whose water is collected,
while settled impurities are flushed out through an overflow
pipe. When the owner is certain of the cleanliness of rainwater,
done by constant visual testing and actual tasting of water,
the overflow is plugged and the Tanka inlet opened. That starts
the flow of the water into the Tanka. The Tanka has a hatch
cover, which is kept closed except for the time when water
is needed. The water retention capacity of these Tankas is
seen in the form of a particular 'danger level' indicated
inside the tank by the depiction of a sculptured 'fish'. Filling
above this mark was considered dangerous as the hydraulic
pressure inside may well exceed the retaining capacity of
the tank wall.
The Tanka water is stored to be used long after
the rains have stopped. The clean conditions of collection
and storage makes the Tanka water a most precious resource
in the hot summer months. Most owners clean the Tanka only
once in 5 to 10 years. The water quality of the Bharuch Tankas
has been tested and found to be potable by W.H.O. standards.
The need of the hour.
If ever an intervention was required to bring
man and nature together again - it is now. The world faces
a great water crisis. UNESCO PARZOR invites researchers and
institutions to work with it and requests financial inputs
for its research and revival of the Tanka system. If you are
interested in donating to help UNESCO PARZOR in further work.
Click here.
Begum Wadi, Bharuch, an excellent example of a Tanka System
