Most colubrids have very similar care requirements and the vast majority will do well with an ambient of around 73-76 F and a hot spot at 85 F. In the past, I used to keep kingsnakes at room temperature and feed them once a week. They always accepted food and appeared to digest just fine. I never had a regurgitation or health issue of any kind. They are a pretty robust snake family.
That said, I feel they greatly benefit from a warm spot. After providing one, I notice my California kingsnakes hug it quite often with an ambient of 75 F, particularly after eating. It does not matter if the hot spot is achieved by a UTH (belly heat) or an overhead heat lamp/CHE. There is nothing special about belly heat, the snake simply needs a source of heat to assist in thermoregulation.
As for water snakes, despite their name and propensity to eat fish, they don't need a huge source of it. Captive water snakes will do just fine with a clean water dish of a size that they can soak in if they wish (per John1982's suggestion). Most keepers I know use the same substrates you would for other reptiles (aspen, reptile carpet, etc.). Personally, I think cypress mulch is probably the best choice. For feeding, the best success seems to come from feeding live fish and amphibians supplemented with mice (frozen or live).