Think about how happy and
healthy your garden looks after a nice rain shower. Why
is that? Well, it’s exactly what nature had intended.
Rainwater has just the right pH and no salts or excess
minerals, so it is exactly suited to help make the
environment your plants need to thrive. Healthy plants
rely on microbial life in the soil, and since rainwater
has no chlorine or chloramine, those microbes will have
the best environment to provide the nutrients your
When you consider all that goes into
treating and pumping the water that comes out of the
tap, benefits of using rainwater are even clearer. On
average, Texans use about 175 gallons of water per
person per day, and up to 100 of those gallons are being
used outdoors. Imagine the savings if these outdoor uses
could be replaced with collected rainwater.
why isn’t everyone using rain? Perhaps some people
consider it too complicated or cumbersome. Others may be
concerned about mosquito breeding — which can be
eliminated with a properly designed system. And some may
wonder if they will have a problem with a homeowners
association. But in Texas, homeowners associations
cannot prohibit rainwater collection. Not only that,
there is no sales tax collected on equipment for
Rainwater catchment for
irrigation is fairly straightforward, and this article
will help you welcome rainwater into your landscape.
While rainwater can be filtered and treated for
drinking, this article will concentrate on rainwater
catchment for watering plants and lawns. We’ll start
with considerations around design; then look at how to
install; and finish up with maintenance and the best
ways to use collected rainwater.
The first step is to figure out how
much water you will need. Even in a high-rainfall area
such as Houston, some gardens drink up thousands of
gallons per month. So think beyond the barrel. The idea
behind rain catch is to capture extra water in the cool
months to have it on hand in summer.
are highly dependent on local climate conditions. Any
garden needs several inches of rain per month, which in
summer can be quite a lot. One easy way to find out how
much water a landscape requires is to compare water
bills from January and July — the difference between the
two will be almost entirely from irrigation.
we want to know how much rain can be captured from the
roof. One inch of rainfall on a 1,000 square foot roof
yields 623 gallons. That’s more than 10 rain barrels!
Average monthly rainfall figures are easily available
Ready for some math? Multiply the rainfall inches, say
in January, by roof square footage, then times .623.
This indicates what can be captured in a normal January.
Here is one example using data from Austin: 1,500 square
foot roof × 2.2 inches in January × .623 = 2,056 gallons
of water that can be collected. Texas A&M has even made
a calculator available online for those who want to take
plant needs and evaporation into account:
Take a look at roof configuration, as it is not
always possible to collect from the entire building —
perhaps one section of the roof drains to the other side
of the house from the ideal tank location. If the house
has many gables, it can require more creative piping to
collect from different parts of the roof. Is it possible
to place the tank a little further from the house or
barn? Yes, piping can be run underground and then back
up to the tank, as long as there is enough of a vertical
distance between gutter and tank.
Of course, a small
roof area will not be able to supply water for
irrigating large tracts of land. And in a low-rainfall
area, it will take a much larger collection surface to
capture enough water even for a small garden. Perhaps a
garage or barn can be added as a rainwater catchment
Let’s look at the example of a
2,000-square-foot collection area with an
800-square-foot garden. In Houston, an 800-gallon tank
would work in a normal rainfall year, but in San Antonio
it would take 1,500 gallons of capacity. And in El Paso
a winter garden could be irrigated with a 1,500-gallon
tank, but it would not be enough to water much in the
Tank size may need to be adjusted for
different factors, such as budget or space constraints.
Remember that gravity rules: the top of the tank has to
be lower than the bottom of the gutter so the water can
flow from the roof into the tank.
Extra capacity is
always good, since rainfall is more and more
unpredictable. And consider using waterwise planting and
drip irrigation, particularly in lower-rainfall areas.
Add more capacity for wildlife and stock watering too,
since rainwater is a great source for any outdoor water
PARTS AND PIECES
Many types of tanks
meet the bill for rainwater harvesting, so it’s good to
understand some of the considerations. Aboveground tanks
are far less expensive than underground tanks, and even
in the event of power failure the water is still readily
available. An underground tank saves space — it can be
placed under a driveway or lawn — but a leak can be very
costly and disruptive to repair. And be sure that any
tank placed underground is designed for that purpose, as
most aboveground tanks are not designed to be buried.
Septic tanks, for example, are not designed to be empty
and may float out of the ground.
tanks, use an opaque tank or else algae will be able to
form — translucent tanks such as the 250-gallon square
totes are notorious algae farms. Many gardeners place a
trellis around the tank, and some tanks are clad in wood
or bamboo. This is for looks, but shading the tank also
helps with cooling in summer.
Stainless steel will
last forever and keep looking great. Poly (plastic)
tanks are economical, but make sure the tank is UV
stabilized or it will deteriorate rapidly. Keep it in
shade to increase its lifespan. Galvanized tanks require
a plastic or epoxy liner, and the lifespan is about as
long as a poly tank.
Check the manufacturer’s
recommendations on a stabilization pad for the tank.
Some manufacturers specify sand pads, concrete or a
captured ring of crushed granite. Remember that water is
8.33 pounds per gallon. A full 250-gallon tank weighs
over a ton and will sink into the ground or lean if it
is not properly placed.
Check building code
requirements. Most cities do not require a permit for
smaller tanks, but many do require one for larger
capacity cisterns. Structure and setback, childproof
lids, and mosquito prevention are the main concerns of
When collecting rainwater for
irrigation, any roofing material is just fine, though
metal roofs are required if the rainwater collection
system will be treated for potable uses.
a must, to capture the water as it leaves the roof.
Place the tank near a downspout and install a
prefiltration system to keep debris out of the tank and
prevent the captured water from developing unpleasant
odors. This is probably the main reason gardeners give
up on using rainwater; even if the plants don’t mind,
the people using the water do.
Heavy rainfall can
exceed the capacity of the tank, so install overflow
piping at least as large as the inlet from the roof.
Screen off all openings to prevent mosquito breeding.
A simple hose valve at the bottom allows use of the
water, but gravity feed is not fast and the water level
in the tank has to be higher than the garden for it to
work at all. Pumps allow for watering raised beds or
areas far away from the tank, and timers prevent
emptying the tank through forgetfulness.
pump outside of the tank can be straightforward with a
few fittings from the hardware store. Many rainwater
collection systems make use of submersible pumps inside
the tank. This keeps the pump out of the way and is less
likely to get damaged.
Irrigation systems can be run
entirely from the rain tank, and today’s irrigation
control boxes are designed with pumps in mind. Any
irrigator or plumber can also add a make-up water valve
with appropriate backflow protection to provide water to
the tank when it hasn’t rained for a while. This should
be set up so most of the tank remains empty, ready for
the next rain event.
Maintenance includes checking
and cleaning filters. With a well-designed and properly
installed system, the tank itself should rarely, if
ever, require cleaning.
LAWS AND INCENTIVES
Every Texas municipality is required to promote
rainwater harvesting throughout the state. This takes
many different forms — from education to rebates to
property tax relief to sales on rain barrels — and
varies by municipality.
Across the state, rainwater
collection components are exempt from sales tax, and
homeowners associations cannot prohibit collecting
rainwater, though they can have input on design and
Rainwater collection has long been viewed
as part of the solution to the water needs of Texas, and
it’s the very best for your plants. So catch the rain
and save it for a sunny day!.