How deep does water have to be so a mosquito can lay viable eggs in it?
Many mosquitoes, such as Culex quinquefasciatus, lay their eggs on the surface of fresh or stagnant water. The water may be in tin cans, barrels, horse troughs, ornamental ponds, swimming pools, puddles, creeks, ditches, catch basins or marshy areas. Mosquitoes prefer water sheltered from the wind by grass and weeds (reference). There are mosquitoes like Aedes taeniorhyncus (floodwater mosquitoes) which can even lay eggs in moist soil (because the eggs need to dry out before they can hatch) which then waits for the rainy season for hatching. These eggs are capable of surviving through summer, winter and spring to find the right time to hatch (reference). Water is necessary during the life cycle of a mosquito but how much is never an issue. Even the top of some mushrooms can be a place for mosquitoes to lay eggs (reference).