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HOME: Projects Main: Rainbarn Construction: Harvesting and Purifying:

 

Rainwater Harvesting Project

 

Loretta and Jeff Hankins

699 Hillview Circle, Dripping Springs, TX 78620

512-461-0492

 

Location: Hillview Addition, Section 1, Lot 12 (10.67 acres), Hays County

 

Construction Start Date: approximately 10/15/96

Completion Date: approximately 3/3/99

 

Water Barn dimensions: 40' x 80' x 14'

Roof collection area: 3240 sq. ft.

Water storage capacity: Design - 20,000 gallons, Useable - approx. 19,300 gallons

Use:  Potable and non-potable via diverter valve before filtration and disinfection

Distribution method: Pumped with gravity assistance to some areas

Disinfection method: Ultraviolet light incl. 20-micron and 5-micron sediment and 3-micron activated charcoal pre-filters

 

Background

 

In the summer of 1996 I attended a seminar on rainwater harvesting at the Lady Bird Johnson Wildflower Research Center in Austin. Two years earlier, we experienced a spring drought and a low water level in our 250-ft deep well. Combine that scare with the poor well water quality due to extreme hardness and sulfuric odor, and you see why we were looking for alternatives. After also researching other rainwater harvesting sources and case histories, we determined that this was the alternative of choice over drilling an 800-900 ft deep well to sweeter water. Furthermore, we did not want to use questionable carcinogenic chemical treatments and didn't want to deal with large filters and water softeners, which consume and discharge huge amounts of salts. So, after completing construction of the collection surface, the water barn, we were ready to begin capturing the Texas hill country's 32-33 inch annual rainfall. Our 3200 square foot roof can potentially capture an average 61,440 gallons per year.  This averages to about 168 available gallons per day.  With our low flow and low flush fixtures and toilets, this is ample supply for the three adults currently residing on the property.

 

System Design

 

Trunk Line SystemI used 4" schedule 40 PVC pipe and fittings for the raw delivery system. Metal strapping and cable support the piping. I used a 1/8" per foot slope in the tubing from the downspout pipes to the tank.

 

I first designed a gutter system based on the seminar suggestions using six-inch thin wall (SDR) PVC tubing. A 1½ inch wide section of the entire length of gutter including the fittings is removed to accept the ends of the 2½ to 3 inch roofing overhang. This system results in an essentially closed gutter and perhaps prevents entry of very large debris objects. However, it is also difficult to clean, if necessary, and it makes a nice place for bugs, wasps, and even birds to hide and nest. So, when it was time to install, I elected to use conventional 5-inch continuous aluminum extruded gutters.

 

Once installed, the first-flush vertical wash pipe system could be installed. The principal of this type of system is based on the fact that the first 10 or so gallons of rainwater washed from the roof surface contains most of the dirt and contaminants that have settled onto the roof and gutters. One of four "First Flush" wash pipe systems Those ten gallons of dirty rainwater are diverted to the vertical tubing and then the additional water that is collected in the gutters flows directly into the tank. I have made improvements in this age-old system so that the system works automatically. These improvements have shown very positive results in continuous and prolonged use.

Ginny Gauge

The "Ginny" gauge measures the level of water inside the tank and displays it in inches. In my 20,000 gallon tank, each 8.5 inches equals about 1000 gallons. Here the gage shows 90 inches, so, 1000 x 90/8.5 = 10,588 gallons.

 

Pump, air tank, and filters

The purification system draws raw rainwater from the tank and then sends soft, pure, clean drinking water to the house. A 1/2 horsepower shallow-well pump draws the water from the tank and pressurizes it to 30 - 40 psig. A 40-gallon air-charged pressure tank and regulator allows water usage without running the pump until pressure reduces to 30 psig. There are two particulate filters in series, rated at 5 and 3-micron particle size, and a disinfecting ultraviolet light rated at 10 gallons per minute flow. The 40-watt light is rated at 9600 hours, or about 13 months of continuous use.

 

There is also a floating filter inside the storage tank. Water is drawn from a port at the bottom of the tank, but a flexible hose is attached to the port on the inside of the tank and connects to a large filter that is suspended by float about 20 inches below the water surface. The cleanest water is always off both the surface and the bottom of the tank. There are also two minor but necessary components; a back flow valve and a manual valve between the tank and the pump.  A supply valve is provided to switch back to the water well during rainwater system down times.

 

 

Elevation Schematic

 

Elevation Schematic
See larger image

 

Site Plan

 

Site Plan 


Water Barn Truss Construction Plan

 

Truss Construction Plan

 

Water Barn Construction Plan

 

Barn Construction Plan

 

Water Barn Elevation Plan

 

Barn Elevation Plan

Cost Detail

Cost Detail

 Major Equipment Detail

 

 

Roofing:

Galvalume, 7/8” high-ridge Cee-panel           

Fiberglass water tank:

Manufacturer: Permian Tank Fiberglass Division

Material: ISO/ORTHO

Ultraviolet water purifier:

                        Manufacturer: Atlantic Ultraviolet Corp.

                        Brand name / Model: Mighty Pure / MP36B

                        Max. Flow: 12 gpm

Water pump w/82 gal equivalent pre-charged tank:

                                Brand name / Pump Model: Flotec / FP4022-00L 24H98U

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