Increased water demand is extremely common following an ashfall, as the cleanup phase begins, and should be anticipated and planned for. Factors that contribute to the level of water demand include the seasonality of the eruption (water demand is higher in summer), the storage capacity available, and the cleanup methods used.
It may be necessary to control water usage to avoid water shortages for critical uses such as firefighting, drinking water and sanitation. Minor ashfalls (<1-2 mm ashfall or <1/16 inch) are likely to lead to only minor increases in water usage and should not require management action, but thicker ashfalls will lead to increases in water usage which may require management actions such as water conservation notices.