The cement bond is easily broken by forces which pull it apart tensile stresses. Thus it is necessary to use a material like steel inside the concrete or plaster for large water tanks. The weight of the water will stretch the tank walls. Barbed wire or weld mesh is heavy enough to withstand the stress and hold the tank together. (Straight wire can be used in place of barbed wire, but the barbs help grasp the plaster, and the two twisting wires are stronger than a single wire.) Chicken wire helps hold the plaster together between the stronger wire.

Although the soil helps support the weight of the water, even the ground hemispherical tanks will stretch when full. Hard rocky soils provide better support. Loose or sandy soils should have more reinforcement (barbed wire) in the tanks.

Upright water tanks receive most tensile stresses in the bottom third of the wall and in the joint between the floor and wall. Extra reinforcement wires in the wall and joint and thickening the plaster at the joint prevent cracking at these points of stress.