This 10,700-gallon
tank was home-built by Mike McElveen from a stock panel form and sheet metal.
Lined with polyethylene film, it stores rainwater for residential
use.Photo by Jan Gerston
An old technology is gaining popularity in a new way. Rainwater harvesting is enjoying a renaissance of sorts in Texas, but it traces its history to biblical times.
Extensive rainwater harvesting apparatus existed 4000 years ago in the Negev Desert. In ancient Rome, residences were built with individual cisterns and paved courtyards to capture rainwater to augment water from the city's aqueducts. And as recently as early in this century, rainwater was the primary water source on many ranches, with stone and steel cisterns still standing today on homesteads upon which wells were long ago drilled.
On small islands with no significant river systems, rainwater is the only source of water. The island of Gibraltar has one of the largest rainwater collection systems in existence.
Now drought-sensitized Texas is waking up to the potential of water literally falling from the sky. In fact, the American Rainwater Catchment Systems Association based in Austin, claims about 50 Texas members, according to vice-president Bill Hoffman. The organization is working on standards for rainwater harvesting systems. (ARCSA). (For information on ARCSA, call Hoffman at (512) 463-7932.
Rainwater offers advantages in water quality for both irrigation and domestic use. Rainwater is naturally soft (unlike well water), contains almost no dissolved minerals or salts, is free of chemical treatment, and is a relatively reliable source of water for households. Rainwater collected and used on site can supplement or replace other sources of household water.
One of the beauties of rainwater harvesting systems is their flexibility. A system can be as simple as a whiskey barrel placed under a rain gutter downspout for watering a garden or as complex as an engineered, multi-tank, pumped and pressurized construction to supply residential and irrigation needs.
Although configurations vary with each installation, most systems include five basic components: (1) a catchment area, which could be the roof of a house or an open-sided barn sheltering cisterns, (2) gutters and downspouts to channel water from the catchment to storage, (3) cisterns and storage tanks, (4) a conveyance system, either gravity-fed or pumped, (5) water treatment.
Cost of a rainwater harvesting system is comparable that of a drilled well and pump. The primary expense is the storage tank. A good rule of thumb is about $1 per gallon of storage, although the cost of components varies widely. Operating costs can be less than those of a well, since rainwater eliminates the need for water softening treatments.
The City of Austin, through its Green Builder Program, encourages rainwater harvesting by including it as a factor in its rating system for environmentally friendly houses. The Green Building Guide rates four aspects of a home--energy, building materials, solid waste and water. The program's Sustainable Building Sourcebook is a clearinghouse of information on state-of-the-art conservation techniques. For more information, call (512) 499-3545.
This 10,700-gallon
tank was home-built by Mike McElveen from a stock panel form and sheet metal.
Lined with polyethylene film, it stores rainwater for residential
use.
Photo by Jan Gerston
Mike McElveen
stands before a fiberglass tank which stores rainwater for garden irrigation at
his home near Oak Hill, west of Austin.
"I'm drinking rainwater, but so is everyone else," McElveen said. "The difference is how far the raindrop travels before we drink it." Without chemical treatment, his drinking water is healthier. It is as much as 100 times softer than well water, with lower mineral content and total suspended solids. To illustrate his point quite dramatically in slide lectures, McElveen shows rain falling into a debris-filled ditch draining into Town Lake, and from there to the A.C. Green Water Treatment Plant, which supplies Austin drinking water.
McElveen's system consists of a 2,000-square-foot galvanized-steel-roofed pole barn feeding water via screened gutters to two large fiberglass cisterns with a combined capacity of 17,000 gallons for residential use. In one of two overflow tanks, McElveen once experimented with growing catfish. Ever the tinkerer, McElveen is testing a new 10,700-gallon stock-panel form and sheet metal tank with a polyethylene liner. A 0.5-horsepower centrifugal pump pressurizes water for household use. Near the vegetable garden is yet another cistern, this one galvanized steel, to collect runoff from the house roof. Tannin from leaves falling on the house roof render the water unpalatable for drinking, so it is used to irrigate gardens. Total domestic storage capacity is 48,000 gallons.
Although Federal Housing Administration guidelines estimate residential use at 100 gallons per person per day, while designing his system, McElveen measured his family's residential water consumption, with little effort at conservation, at 50 to 60 gallons per person per day. In any event, if rainwater is to provide for all household needs, storage must be sized to compensate for the worst-case scenario of high consumption and drought.
For drinking water treatment, McElveen relies on 5-micron and 1-micron cartridge filters and an ultraviolet (UV) treatment. He runs an Environmental Protection Agency test every 8 months for the same contaminants as municipal utilities test for: heavy metals, volatile organic compounds, pH, and hardness. An anecdote McElveen likes to tell concerns the refinancing of his house 10 years ago. The well had been disconnected, and despite the fact that rainwater served the needs of the household, his loan request was denied. McElveen reconnected the well and submitted water samples for testing, but the well-water sample failed its water quality test. McElveen then purified the well water, reconnected the well for just the day of inspection, passed the test, and received loan approval. Ironically, the rainwater which had been serving the family exceeded water quality standards all along.
Since that time, rainwater harvesting has become a more acceptable alternative. Banks are more amenable to grant loans for rainwater-dependent residences. Architects, among them Peter Pfeiffer of Austin, integrate rainwater harvesting systems into design for new construction. And insurance companies, who formerly balked at insuring a house relying solely on rainwater harvesting, thereby effectively denying access to home financing, now sometimes offer a slight discount in light of the ready supply of stored water available to fight fires if a fire hose connection is installed at the storage tank.
This month, Hays County, the fastest-growing county in the nation, will consider an ordinance that would allow for smaller lot sizes in new subdivisions using household rainwater instead of groundwater (and central sewer connections instead of septic tanks). "Rainwater harvesting systems are a factor being considered for a waiver in lot size minimum requirement," said Allen Walther, county Director of Environmental Health.
Using existing gutters on the roof of the adjacent biology building, runoff from the roof is channeled into a 1,000-gallon tank. A float valve inside the tank maintains the proper water level. Overflow is pumped to a small constructed wetland adjacent to the highest pond, from which it trickles down through soil and rock back to the pond. The tank itself is buried within a bermed garden, hidden from view. When the pond water level drops due to evaporation, a sensor triggers a servo motor, which opens a valve to allow stored rainwater to gravity-feed from the tank to the pond. The first flush of water from the roof contains dust, debris, and bird droppings. To separate the first flush from the stored water, a 6-inch PVC vertical standpipe, sealed at the top but with a removable bottom plug, is installed. Only after this pipe is filled will rainwater be routed to the tank.
Rusty Osborne, of
the University of Texas, checks 1,000-gallon tank storing make-up water for
three recirculating ponds.
Photo by Jan Gerston
This small
constructed wetland adjacent to a biology laboratory, receives rainwater runoff
from a small harvesting system at the University of Texas, designed by Rusty
Osborne.
The National Wildflower Research Center, founded by Lady Bird Johnson, finds rainwater best for irrigation. The most prominent feature of the center is the 10,000-gallon limestone-and-mortar tower cistern. Roof catchment areas of more than 20,000 square feet feed into three cisterns and two storage tanks with a capacity of 70,000 gallons. A network of aqueducts transports rainwater to storage.
In fact, many city dwellers served by municipal water districts, while finding they cannot justify the capital costs of installing a system adequate for household use, irrigate gardens with collected rainwater. Many rainwater collection systems complement residential graywater recycling efforts, and in fact, interest in rainwater harvesting is a natural outgrowth of graywater irrigation.
Galvanized steel
tanks, integrated into the aethetics of this demonstration home, provide 13,700
gallons of rainwater storage at the Center for Maximum Potential Building
Systems.
Photo by Jan Gerston
Recently, the Center produced the informative Texas Guide to Rainwater Harvesting under the direction of Gail Vittori, in conjunction with Texas Water Development Board. This 60-page primer emphasizing residential and small-scale commercial applications addresses water quality, cost, aesthetics, demand and collection formulas, and system design. In an appendix are numerous Texas case studies of existing systems using concrete, fiberglass, and steel storage tanks. Some case studies feature composite graywater/rainwater systems.
The centerpiece of the farm's storage is a site-built 40,000-gallon concrete cistern. The unique cistern, designed by Matt Bachardy and Mark Licklider of Sustainable Homesteads, was constructed by first bolting together a form, to which galvanized panels were mounted. Next, a network of reinforcing steel was installed, and the wall and floors of the cistern were covered monolithically with Shot-crete, a proprietary concrete sprayed over the rebar. The forms were removed, then a center structural column was built. Structural beams were installed for roof support. The roof the cistern is bermed to allow it to function as a collection area. This flexible design allows construction of cisterns ranging from 10,000 to 80,000 gallons.
To construct this
40,000-gallon tank at Avera Armadillo Acres, Sustainable Homesteads first bolted
together a frame, then mounted galvanized steel panels to the
frame.
Photo courtesy Sustainable Homesteads
The centerpiece of
the rainwater collection system Avera Armadillo Acres in dripping springs is
this 40,000-gallon site-built concrete tank. This photo shows reinforcing steel
in place before the concrete roof is poured. The rainwater harvesting system at
the organic farm was engineered and constructed by Sustainable Homesteads of
Wimberley.
A proprietary
concrete is sprayed monolithically over re-bar to form the inside of the main
cistern at Avera Armadillo Acres.
A
galvanized-steel-roofed pole-bar constructed over the Avera residence is the
largest rain catchment area. The galvanized steel tanks in the foreground act as
settling tanks.
The cover of the
large concrete cistern is bermed so that it also serves as a collection
area.
Rainwater from a barn and pole barn constructed over the farm's residence is routed first to buffer tanks, where dust and debris settle out. From there, water is gravity-fed to a sump at the lowest point within the system. A float switch-controlled sump pump lifts water into the main cistern. Water treatment is afforded by UV light, a sand filter, a 20-micron cartridge, and disk filters. Water pressure is controlled by a 2-horsepower centrifugal pump and pressure tank. As currently designed, the system is augmented with an existing well, but eventually, rainwater will supply all irrigation and domestic water for the farm. Sustainable Homesteads can be reached at (512) 832-0737.