Third World Water Forum, Kyoto, Japan
Prof : Kavas Kapadia
Professor of Planning, School of Planning and Architecture, New Delhi 110001, India
Topic: Water and Cultural DiversityPreforum Colloquium on Water and Cultural Diversity
Date : Saturday, 15th March, 2003
Convening Organisation: UNESCO, French Water Academy, Japan Centre for Area Studies, National Museum of Ethinology
Built inside houses
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.