How to Build a Circular Form for Cistern

Bend a piece of sheet metal into a circle and cut the excess metal off. Attach one end of the circular metal to the other using sheet metal screws. Create a second circle out of sheet metal with a smaller diameter. The gap between the two circles will form the sides of your cistern.

Create a second circle out of sheet metal with a smaller diameter through the same process as the previous step. The gap between the two circles will form the walls of your cistern.

Place short sticks of steel rebar into the ground within the larger circle. Hammer the rebar into the ground until the rebar sticks out of the ground slightly lower than the height of the base of your cistern.

Pour concrete within the larger circle until you completely cover the rebar to form the base of your cistern. Make sure to stick rebar through the concrete a couple inches from the edges of the large form before the concrete dries. These rods will provide support for the sides.

Place the smaller circle form in the middle of the large circle form when the concrete that forms the base fully cures. Fill the gap between the large and small circular form with concrete to form the sides. You can leave the forms on the concrete or you can remove them after the concrete cures.

If you want to form a concrete lid for your circular cistern, bend another piece of sheet metal into a circle at least 2 inches in diameter over the measurement of the sides so that your lid does not fall into the cistern. Fasten the ends together with screws Since you will have difficulty fitting rebar into a thin lid, place weaved rebar into the middle of the form and pour concrete into the form to your desired lid height. Once dry, you can lift the lid onto your cistern.