This photograph of a Taanka (as it is called in Hindi) or rainwater collection tank, was taken near the town of Sujangarh in Rajasthan, India (in November 2008). This region of (north-west) Rajasthan usually receives scanty rainfall and has saline groundwater. Therefore, people here have been surviving on harvested rainwater for centuries, a lot of which is collected though Taankas and used judiciously in the months following Monsoon rains.
This particular Taanka had a small cemented (catchment) area around it, sloping inwards (towards the round tank). The tank, with a dome-like roof, had an opening on top to draw the collected water out, just like from a well.
Taankas stand as a reminder of traditional, cost effective, time-tested, simple and sustainable rainwater harvesting techniques that have been prevalent in India. It’s a pity that despite their existence, little or no effort to collect rainwater is made locally in India’s towns and cities where availability of water is usually stretched, and despite exorbitant spends on buildings, equipping them with expensive gadgets and digging expensive borewells. A concise writeup about Taanka on Wikipedia is worth reading.