Harvesting Rain in Cochise County

Here is an easy formula:

1. Measure the square footage of the collection area (for example a roof that is 30 feet wide x 50 feet long = 1500 ft²)
2. Multiply the area by the amount of rain in inches
3. Multiply that number by 0.623 (that is the quantity of water in gallons one inch deep in one square foot of space)

This will equal the number of gallons which can be collected.

Landscapes and hard surfaces can be designed and modified to hold, direct and distribute rainwater to plants with rainwater harvesting.

Preventing water from rapidly running off of the landscape is of primary importance. Porous paving materials such as bricks and special asphalt can allow water to penetrate. Angling hard surfaces to drain to planted areas instead of off the property can supplement irrigated areas.

Many backyards of urban properties are bordered by privacy walls. These walls have openings at the base to allow water to drain out.

Partially blocking these openings for a time can hold in rainwater, giving it a chance to soak into the ground. Caution must be taken, however, not to block the escape of the water to the extent that flooding of the home occurs.

As an example: 1,500 square feet of roof area x 15 inches of rain x 0.623 = 14,017 gallons.

Request our water budget calculator by emailing Caitlin Brady at cbrady17@arizona.edu. 

Collection

Multiply the impermeable collection area’s square footage by the rainfall in inches, then take that total and multiply it by 0.623. The answer is total collected gallons for that amount of rainfall. However, be conservative and use 90% of the total to account for losses. For example:

• Roof area = 1,000 sq ft
• Annual Rainfall = 15 inches
• Roof area x annual rainfall = 1, 000 sq ft x 15 inches x 0.623 x 0.90
• = 8,410 gallons/year

Cover all openings of containers with screening to keep out mosquitoes. You can also use a microbial insecticide, specific to mosquito larvae, which contains Bacillus thuringiensis israelensis (Bti). Easy to find in gardening catalogues and in garden departments, often called “Mosquito Dunks”.

Have an opaque container to keep algae from growing. If you need to paint a translucent container (the white plastic ones are not opaque), tinted rubberized roof paint works well.

Pressure

Using the information above, you need to decide if you are going to use gravity or pressurize your water. Drip systems and soaker hoses need 15- 20 psi to work correctly. Methods of irrigation like basin flooding or “T-Tape” (a drip system that functions on 2-10 psi) can be used for low pressure systems. For more information on “T- Tape”, search the web. If you are using containerized water for indoor use, you will need to pressurize the water. 

Considerations

Before you set up a water catchment system, ask yourself a few questions:

System Components for simple, non-potable use, gravity fed system

• Gutters
• Screen
• Container
  • Barrels: Available at feed stores, car washes, web sites.
  • Larger Containers: Potable plastic, metal, fiberglass, ferrocement, septic tanks, corrugated metal pipes (culverts), or? Available at feed stores, tank supply companies (look in phone books), septic system suppliers, building suppliers.
• Tank overflow
• Drain distribution system (gravity flow to landscape)

System Components for complex systems, both potable and non-potable uses

For potable uses: Research carefully all materials used that come into contact with the rainwater. The more maintenance your system receives, the higher the quality of water. 

• Roof Material:  For potable use, metal roofs are preferred that do not contain lead, zinc coatings or copper. Preferred metal roof materials include stainless steel, galvanized steel and galvalume steel. Some other roof materials are acceptable. If coatings are needed, there are roof coating products that are NSF approved.
• Gutters
• Screen
• First wash system
• Large container (see above)
• Tank overflow drain
• Plumbing from tank to pressurizing system: Use Schedule 40 PVC pipe, not copper or ABS
• Pump from tank to filters/pressure tank (minimum 30 psi for inside use)\
• Pumps available at plumbing supply houses, RV dealers
• Filters for sediment
• Final water treatment, such as ultraviolet light