*The water is free; the only cost is for collection and use.
*The end use of harvested water is located close to the source, eliminating the need for complex and costly distribution systems.
*Rainwater provides a water source when groundwater is unacceptable or unavailable, or it can augment limited groundwater supplies.
*The zero hardness ofrainwater helps prevent scale on appliances, extending their use; rainwater eliminates the need for a water softener and the salts added during the softening process.
*Rainwater is sodium-free, important for persons on low-sodium diets.
*Rainwater is superior for landscape irrigation.
*Rainwater harvesting reduces flow to stormwater drains and also reduces non-point source pollution.
*Rainwater harvesting helps utilities reduce the summer demand peak and delay expansion of existing water treatment plants.
*Rainwater harvesting reduces consumers' utility bills.
harvesting can reduce the volume of storm water, thereby lessening the impact on erosion
Wells Branch Municipal Utility District in North Austin captures rainwater, along with air conditioning condensate, from a new 10,000-square-foot recreation center into a 37,000-gallon tank to serve as irrigation water for a 12-acre municipal park
Lady Bird Johnson Wildflower Research Center in Austin, Texas, harvests 300,000 gallons of rainwater annually,
Advanced Micro Devices semiconductor fabrication plant in Austin, Texas, does not use utility-upplied water for irrigation, saving $1.5 million per year by relying on captured rainwater and collected groundwater.
Reynolds Metals in Ingleside, Texas, uses stormwater captured in containment basins as process water in its metal-processing plant, greatly offsetting the volume of purchased water.
On small volcanic or coral islands, rainwater harvesting is often the only option for public water supply, as watersheds are too small to create a major river, and groundwater is either nonexistent or contaminated with salt water. Bermuda, the U.S. Virgin Islands, and other Caribbean islands require cisterns to be included with all new construction.
estimated 100,000 residential rainwater harvesting systems are in use in the United States and its territories (Lye, 2002).
harvesting is encouraged by Austin and San Antonio water utilities as a means of conserving water. The State of Texas also offers financial incentives for rainwater harvesting systems. Senate Bill 2 of the 77th Legislature exempts rainwater harvesting equipment from sales tax, and allows local governments to exempt rainwater harvesting systems from ad valorem (property) taxes.
installation and maintenance costs of a rainwater harvesting system for potable water cannot compete with water supplied by a central utility, but is often cost-competitive with installation of a well in rural settings.
big commercial building, the volume of rainwater, when captured and stored, can cost-effectively serve several end uses, such as landscape irrigation and toilet flushing.
Lye D. 2002. Health risks associated with consumption of untreated water from household roof catchment systems. Journal of the American Water Resources Association 38(5):1301-1306.
Chapter 2 Rainwater Harvesting System Components
slate, metal, clay, concrete for potable harvesting
composite, asphalt, wood, tar, etc should be used only for irrigation [on edible crops?]
storage tank or cistern is dictated by several variables: the rainwater supply (local precipitation), the demand, the projected length of dry spells without rain, the catchment surface area, aesthetics, personal preference, and budget.
Water weighs just over 8 pounds per gallon, so even a relatively small 1,500-gallon tank will weigh 12,400 pounds. A leaning tank may collapse; therefore, tanks should be placedon a stable, level pad. If the bed consists of a stable substrate, such as caliche, a load of sand or pea gravel covering the bed may be sufficient preparation. In some areas, sand or pea gravel over well-compacted soil may be sufficient for a small tank. Otherwise, a concrete pad should be constructed.
Table 2-2. Cistern Types MATERIAL FEATURES CAUTION
Trash cans (20-50 gallon) commercially available; inexpensive, use only new cans
Fiberglass commercially available; alterable and moveable, must be sited on smooth, solid, level footing
Polyethylene/polypropylene commercially available; alterable and moveable, UV-degradable, must be painted or tinted
Redwood, fir, cypress attractive, durable, can be disassembled and moved, expensive
Standard municipal water pressure is 40 pounds per square inch (psi) to 60 psi
Water gains 1 psi of pressure for every 2.31 feet of vertical rise.
achieve proper household water pressure are (1) a pump, pressure tank, pressure switch, and check valve (familiar to well owners), or (2) an on-demand pump.
designed with the pumps at the same level and as close to the storage tanks as possible.
cistern float filter (Figure 2-11) allows the pump to draw water from the storage tank from between 10 and 16 inches below the surface. Water at this level is cleaner and fresher than water closer to the bottom of the tank.
The most popular disinfection array in Texas is two in-line sediment filters - the 5-micron fiber cartridge filter followed by the 3-micron activated charcoal cartridge filter - followed by ultraviolet light. This disinfection set-up is placed after the pressure tank or after the on-demand pump.
Chapter 3 Water Quality and Treatment
[rain is soft water]
if the tank is to supply a drip irrigation system, a small-pore filter at the tank outlet to keep emitters from clogging.
Particulate matter refers to smoke, dust, and soot suspended in the air. Fine particulates can be emitted by industrial and residential combustion, vehicle exhaust, agricultural controlled burns, and sandstorms. As rainwater falls through the atmosphere, it can incorporate these contaminants. Particulate matter is generally not a concern for rainwater harvesting in Texas. However, if you wish, geographic data on particulate matter can be accessed at the Air Quality Monitoring web page of the Texas Commission on Environmental Quality (TCEQ)
Texas Commission on Environmental Quality, Air Quality Monitoring, www.tceq.state.tx.us/nav/data/pm25.html
In agricultural areas, rainwater could have a higher concentration of nitrates due to fertilizer residue in the atmosphere (Thomas and Grenne, 1993). Pesticide residues from crop dusting in agricultural areas may also be present.
In industrial areas, rainwater samples can have slightly higher values of suspended solids concentration and turbidity due to the greater amount of particulate matter in the air (Thomas and Grenne, 1993).
Testing Harvested rainwater should be tested before drinking and periodically thereafter. [quarterly]
Chapter 4 Water Balance and System Sizing
theoretical max of 0.62 gallons per sq foot, but some is always lost
assume an efficiency of 75 percent to 90 percent
In most Texas locations, rainfall occurs seasonally, requiring a storage capacity sufficient to store water collected during rainy times to last through the dry spells.
West Texas, the historic longest span of continuous dry days has exceeded three months.
Average annual rainfall is calculated by taking the sum of historical rainfall and dividing by the number of years of recorded data, National Climate Data Center website
Median rainfall is the amount of rainfall that occurs in the midpoint of all historic rainfall totals for any given month.
Median rainfall provides for a more conservative calculation of system sizing than average rainfall.
A water-conserving household will use between 25 and 50 gallons per person per day [I see ths often, seems high]
study of 1,200 single-family homes by the American Water Works Association (AWWA) in 1999 found that the average water conserving households used approximately 49.6 gallons per person per day (American Water Works Association, 1999).
Hot water on demand
electronic spreadsheet, downloadable in Excel format from the Texas Water Development Board
Chapter 5 Rainwater Harvesting Guidelines
No national standards exist for rainwater harvesting systems
American Rainwater Catchment Systems Association ARCSA website at www.arcsa-usa.org
Rules, ordinances, building codes, and homeowner association covenants nationwide run the gamut from requiring rainwater harvesting systems on new construction to prohibiting tanks as an eyesore.
In Texas, HB 645, passed by the 78th Legislature in 2003, prevents homeowners associations from implementing new covenants banning outdoor water-conserving measures such as composting, water-efficient landscapes, drip irrigation, and rainwater harvesting installations.
Chapter 6 Cost Estimation
[many tables comparing various component costs]
Chapter 7 Financial and Other Incentives
constitutional amendment passed as Proposition 2 by Texas voters in November 1993 exempted pollution control equipment, including water-conserving equipment at nonresidential buildings, from property taxes.
Appendix A References
Appendix B Rainfall Data
Appendix C Case Studies
Walker County Cooperative Extension Office Huntsville
AMD/Spansion FAB25 Austin
water savings has been verified at about 4.75 million gallons per year using online flow meters
water savings from the rinse water reuse system is approximately 210 million gallons per year and had a return on investment of less than one year.
J.J. Pickle Elementary School/St. John Community Center Austin
Feather & Fur Animal Hospital Austin
Pomerening/Dunford Residence Bexar County