The underground water table of Dhaka can be recharged easily during the rainy season by artificially infiltrating water through the topsoil layer of ground into the sub-soil reservoirs, local geologists said. Hydrologists in many countries experiencing rapid depletion of underground water table apply artificial methods to keep their water table healthy and prevent subsiding of the ground. In Germany, coal mine companies practise a cheap, simple yet intelligent method to recharge their sub-soil water reservoirs depleted because of mining. According to the German hydrologists, water is pumped back to the underground reservoir using simple infiltration wells and ditches. The topsoil of the land that grows trees retains water. As a result rainwater cannot recharge a depleting sub-soil water level. The topsoil also retains water from the rivers and ponds. Beneath this level of soil is the sand and silt zone which easily absorbs water and send it to the water reservoir beneath. The German infiltration wells designed by leading mining company RWE are dug like a traditional well through this topsoil, which may be typically 20-30 feet deep. Once the well hits the sand zone, it fills up the well with sand. When water is poured using pumps, the sand absorbs it instantly and sends it to the sub-soil water reservoir. Such a well can pump in millions of cubic metres of water every year. This method can also greatly help recharge Dhaka's water tables fast during the rainy season. According to Dhaka Water Supply and Sewerage Authority (Wasa), the city of 10 million people consumes 75,000 litre water per second using a total of 2,500 deep tube wells of which Wasa owns 800-1,000. The present highest sub-soil water level of Dhaka lies at a depth of 210 feet, which used to be less than 50 feet two decades ago. The Bangladeshi topsoil--called Madhupur Clay Layer--is 10-45 feet deep. Beneath it lies the sand and silt zone called Dupi Pila. Infiltration wells can be dug at a very low cost and these could greatly speed up the water recharging system.