Rainwater storage tanks can be buried below ground 
or placed half way in the ground depending on the site. Rainwater catchment cistern buried below ground - 
Before 5000 gallon rainwater catchment system at SIP office. Rainwater catchment system gutters diverted to underground cisterns Rainwater catchment gutters and underground cisterns. After – Tanks are buried under middle terrace section. Laundry diversion for reuse of washing machine water. Passive Rainwater catchment – Cobble rock placed in 
the bottom of the depression slows and holds runoff 
water from the road and waters surrounding vegetation. Swale used to slow and infiltrate water, native seeding 
and planting to follow. Passive Water Catchment - Gabion rock structures 
holding storm water runoff from parking lot Check dams at SIP office. Rainwater catchment pond and spillway. Greywater infiltration area with fruit trees. Water from roof canal is channeled into perforated PVC 
pipe covered with pumice stone. Rainwater is released to 
roots of nearby vegetation with minimal evaporation. Pumice Wick (before) Pumice Wick Pumice wick completed -- small pea gravel covers drain 
box. Tree roots and grass lawn use captured rainwater 
from the underground pumice wick. Campo Verde constructive wetlands.

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San Isidro Permaculture has been doing high quality, integrated work for years. That's why I've featured their work and consulted their expertise in the creation of my books, "Rainwater Harvesting for Drylands and Beyond." I recommend you do the same."
-- Brad Lancaster
Rainwater Catchment
San Isidro Permaculture can create catchment systems to suit your site and to fit any budget.

Current drainage systems and designs try to quickly direct water off your site to avoid flooding problems. Our approach uses your land to redirect, absorb, and hold rainfall, thereby reducing flooding problems and irrigation needs. Rainwater from a roof can be filtered and stored in rain barrels, underground tanks (cisterns), or aboveground tanks, and then used for irrigation or other outdoor uses. (Also see ferrocement tanks.) Stored rainwater can be easily treated and become a potable water source.

Impermeable surfaces — roads, sidewalks, patios, etc. can be redesigned to infiltrate water or direct runoff to vegetation areas. 
These catchment techniques can decrease your irrigation water consumption while recharging the groundwater table. Vegetation responds more positively to rainwater than treated (city) water due to its low dissolved mineral content and because it has no residual chlorine.

To calculate the amount of water you can store, visit: Volume of Rainfall Calculator

Jeremiah Kidd is an accredited and certified Rain Water Catchment Professional through ARCSA (American Rainwater Catchment Systems Association)

San Isidro Permaculture is a distributor of Water Wall rainwater catchment tanks.

Water Wall Tank