Making a realistic water is not easy. The first step consists in getting the “water volume” necessary. If you want to make a puddle or a small stream, easy. if you want to make a lake or sea, much harder. The best way is to cast some inclusion resin you can find in a DIY store. It’s exepensive and expires very quickly but you have no choice. First yo must mix the two components and cast it in an hermetic form you made before.