Not all snails lay their eggs emmersed. Many will lay them on plant leaves, gravel, or on the glass, it really depends on the species. I've nver had too many snails, but I have a crowd of fish that are pretty stingy about sharing food with something as slow as a snail. Controlling nutrients is the easiest way to control snails, IMO, though removing eggs, and having fish that eat either the eggs or the snails will help as well.
However, if the snails is white, I would suspect that your tank has soft water, low KH? If that's the case, you probably won't have a big problem, since the whiteness indicates that the calcium is being leached from the snails shell. They don't survive or reproduce very well in this kind of water.