Seismic activity continues on Grand Comore as the island struggles to come to grips with the aftermath of Mount Karthala's eruption last week, blanketed by volcanic debris that is threatening public health. The eruption prompted a mass exodus of villagers living in the shadow of the mountain and raised widespread fears that drinking water would be contaminated by the ash and smoke that engulfed the southern part of the island, including the capital, Moroni. Although the smog of ash and smoke has thinned, "a lava lake is forming in the crater - it is confined within the crater but the eruption is not finished, we could have lava flow", Hamidi Soule, a geologist at the Karthala Volcano Observatory, told IRIN. However, more than the threat of lava spilling down the mountain, a lack of clean water has become the island's biggest concern. Deprived of any significant rivers or streams, a large proportion of the population depends on water stored in domestic water tanks. "Many are home-made and protection is very limited - contamination of the water supply raises serious concerns about the availability of potable water in the areas exposed to smoke and ash," said one UN official. Currently in its dry season, Comoros is desperate for rain, not only to replenish its contaminated water supply but also to wash away the toxic volcanic ash covering the island. "It has not rained yet, there is dust everywhere and with the wind it picks up and moves everywhere," World Health Organisation (WHO) representative Dr Mamadou Ball, told IRIN. An initial government assessment on Saturday estimated that 2,000 people had fled the volcano and approximately 123,000 had no clean water supply. Colonel Ismael Mogne Daho, who is coordinating relief efforts at the Ministry of Defence, estimated on Tuesday that 300,000 people had been affected by the eruption, but "The situation has now calmed and people have returned home," he said. The UN Resident Coordinator, Giuseppina Mazza, said around 245,000 people were living in the area exposed to volcanic ash and, based on information from the ministry of defence, she estimated that 175,000 people could be facing shortages of potable water due to the eruption. UN agencies are working with local authorities to deliver water supplies to affected populations. According to a UN official, the United Nations Children's Fund has provided 280,000 liters in the last two days, and the government has requested WHO support to conduct water and sanitation assessments.