How to Use an Old Metal Boiler Cistern for Irrigation

Position the boiler near the home, where the downspouts from the home's eavestroughs can be routed into the cistern. Use a shovel to dig a small depression in the ground and set the boiler in the depression so the cistern is stable. Select a location that is above your garden or targeted irrigation area. You will use the natural force of gravity to power the irrigation system.

Cut off the top of the boiler with a sabre saw or a cutting torch so the top of the tank features a small round opening. Use the disk grinder to remove any sharp edges from the cut edge before proceeding.

Route the downspouts from the home's eavestroughs into the cistern. Cistern placement is the key to this project. You want to hide the tank out of sight, yet still locate the tank so a majority of the home's rainwater runoff is captured by the tank via downspouts. Fasten the sections of downspout together with the hex head sheet metal screws. Fasten the downspout to the home with downspout straps so that the weight of the rainwater doesn't pull it apart during a heavy rain.

Drill two 1-inch holes in the side of the cistern, one just above grade level, and a second hole directly above the first, 2 inches down from the top lip of the tank. The bottom hole is the irrigation access hole, and the top hole is the overflow hole.

Connect a threaded PVC fitting into both of the holes. Seal the fittings in place with silicone caulk on both the inside and outside of the tank. Then glue a 1-inch PVC nipple into each fitting.

Connect the ball cock to the lower PVC pipe, and then another 1-inch PVC nipple, and then a "T" fitting that points upward. Glue these PVC fittings together according the instructions on the PVC cement. Connect PVC pipe between the upper, overflow hole and the "T" fitting on the lower pipe. The overflow water will drain into the irrigation pipe. If the overflow water was allowed to simply drain over the edge of the cistern, it would eventually erode the earth under the tank, and possibly cause the tank to become unstable or tip over.

Using PVC pipe, fittings and PVC cement, lay the pipe on the ground from the cistern to the irrigation area. Glue together each fitting. Use a threaded union fitting for any connection that you want to be able to remove from time to time. Use standard pipe from the barrel to the irrigation area. When you are laying pipe in the irrigation area, perforate the pipe radially with 3/16-inch holes, at a distance 1 to 2 inches apart from one another. Glue a cap on the last piece of PVC pipe.

Use the rain barrel to catch water. When the land needs irrigation, open the ball cock on the cistern, and gravity will carry the water through the irrigation pipes. The perforated pieces of pipe at the end of the line will act as a sprinkler, and distribute the water evenly across the irrigated land.