Walls of water, also called water teepees, are used to protect warmth loving plants from colder temperatures. Unlike a cold frame, a wall of water uses water as an insulator. Often, backyard tomato or pepper growers use walls of water to keep their plants warm in the spring time. But you can only fit one plant in a wall of water. Cold frames, on the other hand, create a warmer environment for groups of plants and use glass, polycarbonate or other plastics as a barrier to the elements.