Assessing Feasibility of Large-scale Rain Harvesting

Two new UA Cooperative Extension fact sheets encourage rural homeowners to consider rain harvesting for their potable water supply

Choosing Large-scale Rainwater Harvesting for Potable Supply

by Mary Ann Capehart and Dr. Susanna Eden

Preparing Rainwater for Potable Use

by Mary Ann Capehart, Dr. Janick Artiola, and Dr. Susanna Eden

Choosing Large-scale Rainwater Harvesting for Potable Supply Abstract

As groundwater becomes harder to access in many areas of Cochise County, risks and costs associated with groundwater wells have become an important economic consideration for small-acreage property owners. Groundwater is considered a non-renewable water supply when aquifers do not recover enough from pumping to reliably produce water from the same level through time. Water may refill the aquifer very slowly, so slowly that the groundwater being pumped today may be thousands of years old. Once more water is pumped than is recharged, an aquifer is in overdraft, with multiple potential negative effects, including the water level drops that have affected the water supplies of individual small-acreage landowners.

Some property owners have turned to large-scale rainwater harvesting to supplement or replace well water supplies. Rainwater is renewable and can be a realistic source of water for homeowners living in remote areas. There are many reasons to turn to harvesting rain for potable water supply. Some homesteaders who purchase land without a well decide that it is less risky to install a rain harvesting system than to drill for groundwater that may be inaccessible at a reasonable depth and cost. Others have a low-yield or seasonally dry well and choose not to deepen their well because they worry that the water level may fall below the new well before they can afford to drill again. Water harvesting is an alternative to having water trucked in. Other people find that the quality of their well water is unacceptable for potable use, and a growing number of people prefer the taste, softness and purity of rainwater over groundwater. Rainwater is generally free of the problems that occur in groundwater, like minerals, common in Arizona groundwater, and contaminants that find their way to groundwater from various sources of pollution.

This fact sheet helps small-acreage landowners consider the option of large-scale rain harvesting to supply water for their domestic needs. Five factors important to assessing whether a rain harvesting system is appropriate are delineated; the basic components of a rain harvesting system for potable supply are briefly explained, and examples of actual rain harvesting systems used by residents harvesting rain for potable use are included, with system data that demonstrate the factors involved in choosing large-scale rain harvesting for domestic potable use.

Look for this fact sheet late fall 2020 at https://extension.arizona.edu/pubs

Preparing Rain for Potable Use Abstract

Rainwater is high-quality water that can be treated to drinking water standards by rain harvesters themselves on their homesteads. This fact sheet guides the layperson through the steps, components, and principles necessary for the safe treatment of collected rainwater to help with those in rural areas where rain is the preferred or the most expedient water supply.

Look for this fact sheet late fall 2020 at https://extension.arizona.edu/pubs

The fact sheet reviews four factors that are critical to the decision to choose rainwater for sustainable, potable supply.

Adjust capacity by:

Adding more roof area (like a porch or shed roof)
Using less water
Adding cisterns (to ensure enough capacity to get through a typical dry season)
Having sufficient rain stored prior to relying on this resource

The fact sheet details a 3-prong treatment which ensures that filtered and disinfected rainwater is safe to drink: a treatment method adequate for most rain harvesting systems.

Three steps:

5-micron sediment filtration
3-micron activated charcoal filtration
UV lamp for disinfection

Click the graph
for an interactive view!

Challenges:

drought
future precipitation variability
perceptions of there not being enough rainfall
upfront costs in the price range equivalent or less than a new well (see specifics in the fact sheet). Costs are significantly less going forward.

Benefits:

soft, generally high quality water
alternative or addition to well water supply in areas with severe groundwater draw-down, such as parts of Cochise County
water supply in areas outside of water utility service with very deep water table levels, such as parts of Coconino County
the conservation of non-renewable groundwater

Water Wise's Off-the-Grid tours showcase homesteads whose demand is supplied with rain only.

A rain roof on a utility shed adds enough roof area to make harvesting rain for all potable demands feasible on this homestead.

ADWR Dry Well Data: 'exempt' wells that have gone dry- reveal the impacts of lowered ground water levels. (Self-reporting has not been robust, ADWR, Sept 20, 2020.)

Sulpher Springs Valley, AZ. Jessica and Jim Bonilla's hand-built earthbag cistern (in-progress in photo) will have the capacity to store 13,000 gallons in an area with 13" average annual rainfall.

Near Bisbee, AZ. Adrienne and Bob Harris harvest rain from 2,660 sq. ft. of combined roof area into two 2500-gal tanks, a 1500-gal, 1300-gal and 420-gal tank with 18" average annual rainfall .

Tucson Mountains, AZ. Retired biologist Jay Cole with their rainwater treatment system which filters water from a 26,000-gal. underground cement cistern from 5,250 sq. ft. of roof with 12" average annual rainfall.

Near Austin, TX Residential rainwater treatment system with a 10 micron sediment filter (a 20 - 10 micron dual gradient filter), a 5 micron activated carbon filter, and UV lamp. Photo: Chris Maxwell-Gaines

We drink our treated rain!

Near Williams, AZ. 15,000 gallons of storage (tanks on the right) and a 300-gal settling tank (tank on left) store rain from 3,069 sq. ft. of roof area with 12" average annual rainfall. Groundwater is found at this location and surrounding areas at approximately 3,600 feet below ground. Photo: Thad Johnson

Banner photo: Derek and Hannah Howlett's homestead with a 28,000-gal steel tank. Courtesy of Derek "Handeeman" Howlet. To learn more about their rain harvesting system, click play.

THE TEAM: Mary Ann Capehart is the coordinator of the Water Wise Community program whose mission is to help those in the Upper San Pedro River Watershed, and others around Cochise County, conserve water and care for all natural resources. She had the privilege to work with co-author, Dr. Susanna Eden, at a student job at the Water Resources Research Center during graduate school, assisting on outreach publications. Dr. Susanna Eden, Assistant Director, WRRC, collaborates on development and implementation of research and outreach programs with relevance to Arizona water resource policy and management among other projects and responsibilities. Co-author, Dr. Janick Artiola, SWES (retired) is a specialist in analytical, soil and water chemistry. Dr. Artiola also worked as a consultant and peer reviewer on a variety of waste management, hazardous waste evaluation and cleanup programs for industry and government agencies. As a Cooperative Extension specialist he taught workshops on Domestic Well Owner care including water quality and treatment where he contributed significantly to Water Wise programming and met team member Mary Ann Capehart.