Drains are generally constructed structures to convey stormwater, waste water, or other sources of water by a flow path or formal channel from a catchment or source to a discharge point. Drains can be part of an organised drainage system or a specific measure to drain depressions or temporary flooded areas. Generally drains in small catchments in undeveloped areas only convey water during or for a few hours after rain, and if they have adequate slope, dry up soon after the rain ceases. However drains with larger catchments or from perennial or artificial sources of water, contain water for relatively long periods and can be significant sources of mosquitoes.