W-7 is the watershed designator of the Otis Creek Reservoir which supplies the City of Eureka with drinking water. Eureka also provides water to Greenwood Rural Water systems one and two. Located Northwest of Eureka about 12 miles on private rangeland, W-7 is the source of some of the cleanest water naturally available in Kansas. To help protect the pristine condition of the water, the lake is off limits to the general public and boating and fishing are prohibited. The city has a Source Water Protection Plan filed with the State which details any possible sources of contamination. There are not many but this plan lays out response measures to be taken in the event some sort of contamination becomes evident.