hydrogamy

As a noun hydrogamy

is (botany) pollination by means of water.

As an adjective hydrogamous is

of or pertaining to hydrogamy.

As nouns the difference between water and hydrogamy

is that water is a chemical, found at room temperature and pressure as a clear liquid, having the formula H₂O, required by all forms of life on Earth while hydrogamy is pollination by means of water.

As a verb water

is to pour water into the soil surrounding (plants).

In botany terms the difference between pollination and hydrogamy

is that pollination is the transfer of pollen from an anther to a stigma; effected by insects, birds, bats and the wind etc while hydrogamy is pollination by means of water.