Rainwater Harvesting Texas

Gutters and Pipes 

Typically roof water is collected first in gutters and conveyed to the tank or cistern by pipe.  In the dry system, the pipes are overhead and drop into an above ground tank through the top and then down to the bottom and turn up or terminate in a calming inlet.  This technique keeps the sediment at the bottom and displaces the stored water in the tank with each new rain event.  If there is enough collected water, the stored water then overflows out the top of the tank.  With this method the floating debris is skimmed off the top and the water remains fresh.  In poorly designed systems, the conveyance pipes drop the newly collected rain into the top of the tank and, if the tank is full, the fresh water is overflowed directly back out and, since the rest of the design is probably also poor, off the property.

Well designed systems that are intended for inside use, whether drinking or secondary, should have some type of first diverter or roof washer and, perhaps, a screen of about 40 mesh or other debris catcher.  The best diverters will capture the first ten gallons of water collected from each 1000 square feet of surface and drain that water to a rain garden, swale or basin for irrigation.  The better cistern pre-filters are self cleaning, ejecting the debris into the overflow or directly onto the ground.

Wet systems convey the collected water from the gutter through sealed pipes that begin at a point about 18 to 24 inches higher than the tank overflow so that the pipes can then travel underground to a tank that is not necessarily adjacent to the collection surface.  This is especially helpful for downspouts at far corners or at the front of the house where overhead pipes could be considered unsightly.  In order to avoid the possibility of draining the tank in the event the pipes develop a leak, the underground pipe rises up and enters the top of the above ground tank, and then drops back to the bottom to the calmed inlet.  A small hole is drilled in the upper elbow inside the tank so that a small amount of water escapes during a rain event, but simply falls into the tank, but if a leak develops in the underground pipe, air will enter the small hole and break the siphon.

With underground cisterns, the conveyance pipes should begin about three feet above grade and then travel to the cistern with a 1/4 inch drop per foot.  If the cistern is a distance from the collection surface, the drop could mean the pipe enters the cistern below the overflow.  This is not a problem, but in colder climates the pipes should be buried at a depth below the frost line to avoid a plug of ice forming in the pipe when the tank is full.  Otherwise snow on the roof could melt and overflow the gutters or back-up under the shingles.  Likewise, in colder climates, the underground cistern should have a separate vent to allow air to enter and escape the tank in the event a plug of ice forms in the overflow.

Wet type conveyance pipes can sometimes also act as distribution pipes when the tank is far from the roof.  A riser can tee into the conveyance pipe and have a faucet above ground at convenient locations along the pipe.  With this arrangement, the conveyance pipe enters the tank at the bottom and turns up with no siphon break.  Only secondary water is available at these hose bibs since there is no floating intake attached to the conveyance pipe.  The danger is that if a leak develops or the faucet is not shut tight, the tank could empty.

French drains and sumps

Another type of system uses French drains and a sump pump to convey rainwater to a tank.  Gutters are not necessary but can be used with rain chains or downspouts leading to the French drains with corrugated, slotted drain pipes covered with angular stone and leading to a small sump equipped with a pump and float switch located underground.  The pump can convey the water to remote locations or higher elevations that would not work with gravity.  This type of system is best in areas that have rain events that are not as intense and the water should be used only for irrigation since surface water will also enter the drains.

EPIC™ System and Gravity 

This is a clever system that combines the storage, conveyance and distribution components into one integrated design that takes full advantage of gravity.  It is only useful on relatively flat sites, especially sports fields and large turf areas.  With this system the turf or sports field itself is the collection surface.  The rain percolates through the underlying prepared media or sand to a layer of D shaped corrugated pipes that are slotted only on the upper portion so that water collects and remains in the lower portion, is distributed throughout the system and, when full, overflows at a low point in the design.  The collected water is then drawn by capillary action back up through the media to the root zone of the grass.  Because the water is coming from below, the grass extends its roots deeper than when watered only from above.  This creates a much more robust root system that allows the grass to survive drought better.

Applied fertilizers are contained in the system and utilized until exhausted rather than running off as pollution.  If a rain event doesn’t occur before the system runs dry, stored rain or recycled water can be fed by gravity into the pipes and 50% less water is needed to do the same job as when applied with conventional sprinkler heads.  Another benefit is that soil compaction from heavy traffic is not as likely to occur as with shallow root systems watered from above.  Many of the newer professional sports stadiums and golf courses are using this system.

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