The Solomon Islands Red Cross says 52,000 people have been affected by the flash floods that destroyed much of the infrastructure on the main island, Guadalcanal.
The aid agency is warning it could take up to a week to reach all the communities there. The death toll from devastating flooding on 3 April stands at 23.
Deputy secretary-general Clement Manuri said on Wednesday the floods have taken a toll on much of the population and the Red Cross is waiting to hear back from volunteers who have moved out into the eastern part of the island.
Mr Manuri says when they return the charity will have a better idea as to the extent of the damage. Two water purifying machines are being used to clean the drinking water and transport it to evacuation centres.
About 10,000 people have sought shelter in 24 centres around the capital Honiara since the flooding.
The National Disaster Council, which is coordinating emergency relief efforts, says there is no threat of further flooding and those who can safely go back to their homes should do so. Officials can then start to deal more effectively with people whose homes have been completely destroyed.
Director Loti Yates said on Wednesday that 40 percent of Honiara remains cut off from its water supply, including many of the evacuation centres where sanitation is a problem, and there is concern about outbreaks of disease.
Australia said it is boosting its aid package for the Solomons to $3 million, most of it to provide food, drinking water, shelter and sanitation.