The architecture of water
How local technologies makes life in an extreme environment liveable
By Anjali Mathai and Liva Shrestha
Jodhpur, December 201

Desert ecosystems are typically known for their water scarcity. The people of the Thar have proven that careful community management of water and other resources makes life in such harsh conditions possible. They make the most of their water resources through age-old indigenous harvesting structures.

One example of such a water harvesting structure is a nadi. At first glance a nadi  seems like an ordinary water body, perhaps only unique because of the rarity of such bodies in a region that otherwise lacks them. But there is a lot more to it than what meets the eye. It is a specially-created piece of landscaping that makes water more available in a water-scarce region. Nadis are man-made village ponds; the one in Daukiyogi Dhani Chira flows in a twisting curve and is about 20 feet deep at its deepest . Nadis are usually located in a catchment area found at the bottom of a gentle slope of land. But they cannot be built in just any catchment in any part of the desert; the soil needs to be a mixture of clay, limestone, and a kind of small gravel. In order to test whether a particular piece of land – that is common to the village and not privately owned – is good for a nadi or not, a test well is dug and some water is poured in to determine whether the retention rate makes the site viable.

What makes nadis unique is that they were developed centuries ago  and that they are still in use today without many additions that may be called ‘modern’. The other is that the people who design and build them are locals. A carefully-planned nadi – which is entirely rain-fed – can become a source of drinking water for both humans and animals for two months to a year after the area’s short but intense rainy season.

But nadis are not only constructed by local norms – they are also governed by them. For example, the Village Development Committee (VDC) in charge of a particular nadi – which is usually used by more than one village in a particular area – oversees its construction and is in charge of maintenance work, particularly the de-silting that needs to be done every three years. The VDC’s most important task, however, is to manage the use of the nadi’s water supply – for example, authorising the transport of any water out of the nadi when the need arises. They also set rules to keep the water clean, allowing it to be used only for drinking; and even though cattle are allowed to use the water for this purpose as well, sheep are kept away since mucus from their noses are known to contaminate water. Also, the area around the nadi is kept free of any shady trees to discourage cattle herds from lingering around after they have quenched their thirst so that they do not litter the area with dung.

Another water harvesting system that has helped the people of the region become more self-sufficient where water is concerned is the tanka, or circular water conservation tank, where water from an elevated artificial catchment is collected during the rainy season. In addition, should they need replenishing during the dry seasons, they are re-filled with water from nadis, beris, and other sources.

Tankas are constructed by the villagers of a particular area and are made mostly of locally-available materials; NGOs like the Gramin Vikas Vigyan Samiti (GRAVIS)usually only provide a few materials not available locally or easily. Tankasappear to be a very sustainable form of water harvesting because they are simple and cost effective to construct yet serve their purpose effectively.

They are usually built ten feet below ground level , two feet above and measure ten feet in diameter. There is a specific procedure involved in their creation. Firstly, the land is sited according to the needs of the community and a ten-foot-deep round pit is dug; the excavated soil is used to create the catchment area. The sides of the pit are then built with red sandstone blocks and the bottom is preparedb by lining it with more sandstone, making sure that it is hammered into the ground securely. A layer of gravel is added to that and held together with more of the cement-lime-sand mixture.

Finally, the part that is above ground is built. The sides are built of sandstone blocks and plastered with cement on the outside. Two rectangular openings are made in the wall a few inches above ground level - one for intake of water from the catchment and the other for overflow of water from the tank , with the latter acting as a pressure relief mechanism in case the tank fills to over-capacityduring a season of unusually high rainfall. There is a depressed channel on the catchment area, at the water intake, consisting of staggered bars (as shown the picture); this feature de-silts rainwater flowing through it before it enters the tanka.The intake and overflow openings are also covered with a wire mesh to prevent mice or other small desert creatures from entering the tanka. The tanka is then covered at the top with sandstone slabs and plastered on the outside.

The tankas created and used today have a long history in the Jodhpur region. They have been specificallydesigned to be another effectiveway to collect and store rainwater for household use.  According to Mr. Rajendra Kumar, Programme Coordinator with GRAVIS, NGOs and government organizations have tried building big tankas that hold up to one hundred thousand litres of water, but structural flaws in those designs demonstrated that they were impractical for several reasons. The first of these is that a larger tanka would need more water to fill up to a depth necessary to make it viable as a source from which to draw water. This is not possible given the amount of rainfall western Rajasthan receives per year – 200 milimetres on average – making a large tanka unsuitable as a water-harvesting system for the region. In addition, it was seen that larger tankas developed cracks along the sides and that fact, along with higher maintenance costs, meant that those designs were abandoned.

The tanka plan currently in use can store up to 20,000 litres of water at full capacity. These tankas are able to serve the requirements of the community effectively.

Another mechanism used to collect drinking water is a beri, a type of well that can also be called a step-well if there is a flight of stairs leading down to the water’s edge. Beris are often built on one side of a pre-existing water body from which the water has percolated to sub-surface levels.

Some beris that are more productive – meaning that the water table in their area is higher than others – are surrounded on four sides by a wall. They are also either covered or built under shady trees to minimise evaporation losses and to prevent sand and rocks from falling into them. They need to be de-silted periodically.

Some beris can hold up to 250,000 litres of water, which is a year’s supply for ten families.

Nadis, tankas,and beris are examples of structures that demonstrate how water – a scarce resource in many places, including the Thar, can be harvested. Their effectiveness shows that indigenous technologies, when combined with effective community management practices, makes it possible for human life to thrive in an extreme environment.