The World Health Organization issued new guidelines on Tuesday on preventing contamination of drinking water supplies and resultant illnesses.

Only 50 percent of the world’s population has access to running water at home, with the rest relying on wells or rivers, according to the WHO.

The U.N. agency’s updated guidelines aim to help authorities improve water quality from the source to the tap or rural well.

“No country, not even a developed country, is immune to problems related to water quality. All regulatory authorities must remain constantly vigilant,” WHO’s Jose Hueb told a news briefing.

The guidelines include instructions on ensuring reservoirs or wells avoid the risk of contamination from human and animal waste, as well as basic advice like regular changing of water filters.

The new guide follows the discovery in Bangladesh that water delivered by tube-wells is laced with high levels of naturally occurring arsenic - putting the health of millions at risk - and recent cases of water-borne bacteria in Canada and in the U.S. state of Ohio.

The guide includes advice on handling humanitarian crises such as in Darfur in western Sudan, where a hepatitis epidemic due to poor sanitation has struck 4,524 people, killing 73. Another 1,292 cases and 42 deaths have been reported among refugees in eastern Chad who fled the violence in Darfur.