Care International has warned of a cholera outbreak in Baghdad unless the coalition forces restore Iraq's water authority.
Cholera has been confirmed in Basra, Iraq's second largest city and Care fears the capital could follow.
"The primary threat to the delivery of safe drinking water in Iraq is the total absence of direct government support and supply functions. This vacuum must be filled now," said Margaret Hassan, director of Care Iraq.
"Many people do not have access to safe drinking water and human waste is flowing from the drains in many parts of Baghdad."
Iraq's water authority is centralised and some staff in Baghdad have not been paid for two months, the organisation claims.
The aid agency hopes last week's United Nations resolution to lift sanctions on Iraq could lead to an improvement by involving the UN in the rebuilding operation.
Care is working alongside the Red Cross and Unicef to assess water and sanitation installation in the war-torn country.