Availability of potable water under emergency situations like flood will soon be a reality. For researchers of the Geo-Environment Division of the National Environmental Engineering Research Institute (NEERI) have come up with a water filter for such purposes. The water filter, called NEERI-ZAR and designed by Mr Subhash Andey, Mr Prakash Kalker and Mr Madan Nanoti has already received the Nina Saxena Excellence in Technology Award at the IIT-Kharagpur this year. The water filter unit, based largely on the principles of slow sand filtration, comprises two plastic containers placed at elevation differences to manage gravity flow. The top container, made of plastic or ferro-cement, stores raw water mixed with an oxidizing chemical preferably potassium permanganate. The second container into which water from the first flows consists of a sand filter and a fixture. Water seeps into the second container and is collected in a third container. The filtered water is disinfected in the third container and is then made ready for use. In the second container, the filter bed consists of a nylobolt cloth placed five to ten centimeters below the sand layer. The filter bed is cleaned when no water flows into the third container. One hundred litres of water can be treated and be made ready for usage in eight hours by the NEERI-ZAR. According to Mr Andey, a researcher and team member of the project, water filter in this case differs from the conventional sand filters because of its ability to wash only the nylobolt cloth and not the entire sand filter. Assuring that having a nylobolt cloth placed around five to ten centimeters of the sand layer will not affect the quality of water, Mr Andey said pollutants do not percolate more than five or ten centimeters of the sand level. Stressing on the benefits, the researchers claim water treatment can be done without electricity and is gravity operated. The water filter, introduced almost two years back and priced around Rs 6,000 per machine, makes it easy for use in villages, particularly in times of flood.