The Marshall Islands Environmental Protection Authority says Majuro's fresh water system and lagoon waters have shown high levels of contamination.
An authority test recently showed 40 percent of the more than 30 water samples taken from the city fresh water system in the capital is contaminated with faeces or other pollutants.
A majority of Majuro lagoon sites tested also showed they were unsafe for swimming and fishing.
The Authority has advised people to boil water thoroughly before drinking.
Our correspondent Giff Johnson says that this is an ongoing problem in the Marshall Islands.
"We have a city water system where water is only on two or three days or part days a week and so what ends up happening with the fresh water is it's pumped out on Monday, Thursdays and Saturdays for a few hours each day and the rest of the time there is no pressure in the pipes and so contamination creeps in and there are all kinds of problems associated with standing water."