what is the best way we can close our water tank in terrace so that no insect n

Dear  Ramachandran

                I think you have either RCC OVER HEAD WATER TANK OR brick wall water tank at terrace. On top of water tank lay RCCslab with csat iron frame for openin, after finishing fit the cast iron lid in the frame. In this way there is no any chance of insects to enter in the water tank. OR use plastic/ sintex water tank.