To store rainwater underground you need proper digging, a tank built for burial, and a pump to get water out. Dig below your local frost line to prevent freeze damage. Use a tank rated for soil pressure on all sides. Add a submersible pump in the tank to push water up when you need it.
I toured a neighbor's underground rainwater tank setup last year and came away impressed. You would never know 3,000 gallons sat under their back lawn. The only sign was a small hatch flush with the grass. They told me their water stays at a steady 55 degrees all year. Above ground tanks heat up in summer and freeze in winter.
The buried cistern installation process starts with digging a big hole. You need to go below frost depth plus room for a gravel bed under the tank. Leave space on all sides for backfill that supports the tank walls against soil push. Most home jobs need a backhoe or small excavator. Hand digging takes too long for anything but the smallest tanks.
Not every tank works for underground rainwater tank use. Burial-rated tanks have thick walls made to handle dirt pressing in from all sides. Standard above ground tanks will crack or crush when buried. Look for tanks marked for underground use with pressure ratings that match your install depth. Common choices are heavy plastic and fiberglass. Some folks use poured concrete for the longest life.
I talked to several contractors about costs before my neighbor picked one. Professional buried cistern installation costs between $8,000 and $25,000 based on tank size and site. Tank sizes for home systems range from 1,000 to 15,000 gallons or more. Smaller tanks fit tight lots while larger ones make the dig cost worth it. Budget for the pump, pipes, and electric work too.
Your submersible pump sits inside the tank and pushes water up through a pipe to grade level. These pumps need electric power, so plan your wire run from the house. Add an access hatch big enough to pull the pump out for service. You also want a way to look inside and check water level. Some folks add a float gauge that shows level from the surface.
Check your soil and water table before you commit to going underground. High water tables push up against buried tanks. An empty tank can float right out of the ground in wet soil. Sandy ground drains well but gives less side support than clay. Get a soil test and groundwater check from a local digger who knows your area. This homework up front saves you from costly surprises later.
Read the full article: Rainwater Collection Systems for Beginners
