Reptiles do not have to return to water to lay their eggs because they produce eggs that are already contained with liquids.
The babies must be able to hatch themselves then return back to the water, why have the eggs be in the water and then have the baby reptile be exposed to such an environment so quickly?
Hm, there is no definite answer according to my research that I've done, possibly check out your local library.
Savannahs are usually large areas of open land with few trees. This area is different from deserts because they receive more rain which allows grasses to grow, unlike desserts.