The Yellow Quill First Nation in east-central Saskatchewan was able to lift a boiled-water advisory after nine years in 2004 because of the efforts by the Safe Drinking Water Foundation, a non-profit organization based in Saskatoon. Hans Peterson and his group designed a water treatment system that first filters water through biofiltration, then treats it a second time by reverse osmosis. The foundation also recommended that Yellow Quill change its source of water from the Pipestone Creek to a deep-water well. Solving the water problems at Yellow Quill became urgent when crises in other parts of Canada occurred after the original boiled-water advisory was issued in 1995: seven people died and hundreds became ill in Walkerton, Ontario, when the town's drinking supply became contaminated with E. coli in May 2002; a year later, in April 2003, thousands of people in North Battleford became ill after their drinking supply was contaminated by cryptosporidium. Groups from several countries, including China, with large rural populations and drinking water problems have shown interest in Hans Peterson's simple and relatively inexpensive water treatment solution.