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San Antonio Answers Rising Water Demand with Source Diversification

City water utility addresses challenge of rapid population growth and diminished precipitation with brackish water desalination, expansion of regional water networks and wastewater recycling.

San Antonio
Tourists enjoy a cruise along the San Antonio River Walk. The river’s flow is maintained using recycled SAWS wastewater. Source: www.thesanantonioriverwalk.com
This March, CNNMoney reported that San Antonio, Texas is the fifth-fastest growing city in the United States. Throughout the 20th century, San Antonio relied solely on the Edwards Aquifer for its drinking water and still depends on it as the main source of its water. The more than 115 new people per day living in San Antonio would increase stress on the municipal water supply in any situation, but a relentless drought in the aquifer’s recharge zone, a 1993 state law that places a 400,000 acre foot (an acre foot is 325,851 gallons) per year, aquifer-wide limit on withdrawals and sharing the aquifer with the country’s fastest growing city, Austin, compel the Alamo city to diversify its water sources.

The San Antonio Water System (SAWS) refers to San Antonio as “water’s most resourceful city,” and SAWS water conservation programs have succeeded in reducing per-household demand by 35 percent compared to historical levels. Marginal returns on further demand reduction efforts, regional population growth and a projected ten percent decrease in current-source availability compel SAWS to increase supply. As Kelly Frazier, executive director of the Texas Desalination Association frames the issue, “When it comes to San Antonio and water, we need more. What else needs to be said?” San Antonio’s city council and SAWS have responded to the water supply challenge with infrastructural, political, and economic solutions.
 
Desalination: Big and Fast
The most ambitious component of SAWS’s multifaceted plan for expanded water supply is the brackish groundwater desalination plant that the utility began constructing this July at the existing Twin Oaks Aquifer Storage and Recovery facility. The desalination plant will use reverse osmosis to produce drinking water from the moderately saline Carrizo-Wilcox Aquifer. SAWS expects the facility to be the largest inland desalination plant in the US when it begins filtering groundwater in October 2016. The facility will initially produce 1,120 acre feet of drinking water per month, but the $441 million, three-phase project expects to produce an additional 1,120 acre feet per month upon completion of the second phase in 2021 and a total of 2,800 acre feet of water per month by the end of its third phase in 2026. The highly saline byproduct of the reverse osmosis process will be stored in subterranean wells onsite. The completed project will produce enough potable water to support 100,000 additional San Antonio households. The Twin Oaks desalination facility will diversify and significantly increase San Antonio’s drinking water supply, but if population growth and water usage per household continue at their current rate, the facility will only meet the drinking water needs of three-fifths of new San Antonio households in 2026.

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An aerial photograph of the Twin Oaks facility where SAWS will construct its brackish groundwater desalination plant. Source: www.edwardsaquifer.net
 
Regional Cooperation: Net Benefits for Neighbors

By expanding cooperation with neighboring municipalities, SAWS has already secured its largest non-Edwards Aquifer water source to date. The new source is surplus water from the Schertz-Seguin Local Government Corporation, a joint project of two south-central Texas cities. SAWS began purchasing surplus water from the corporation in December 2013. The San Antonio utility significantly increased regional water production and delivery capacity this July by constructing a new well field, pump station, supply and delivery pipelines 50 miles east of San Antonio in Gonzales County.

In addition to the revenue San Antonio’s neighbors receive for selling surplus water and renting pipeline to SAWS, these smaller municipalities can purchase water from the newly constructed SAWS pump station. The regional project cost SAWS $149 million and will provide 1,680 acre feet of drinking water per month, enough for 60,000 additional households. The project also enables SAWS to purchase and transport an additional 460 acre feet of water per month from neighboring municipal water systems.

Despite the mutual benefits of regional water cooperation, the political necessities of relationship building and negotiation make regional cooperation a lengthier process than deciding to build new infrastructure in a utility’s existing jurisdiction. SAWS president Robert Puente stated that the project was “ten years in the making.” Charles Porter, a water policy professor at St. Edward’s University in Austin, advises water managers to plan to spend ten to fifteen years negotiating projects that cross multiple jurisdictions.

Recycling: Crisis Averted?
Before SAWS began its supply expansion projects, the utility’s wastewater recycling program began easing the burden on San Antonio’s water supply in 1996. By using filters, aeration, and microbe decontamination, SAWS not only transforms wastewater into sanitized water for agricultural, industrial and recreational use, but also obtains bio-solids which it sells as fertilizer and methane gas which it sells as an energy source. The SAWS recycling program saves nearly 2,135 acre feet per month of water that would otherwise be drawn from SAWS potable water sources. Recycled water travels through more than 130 miles of specially designated municipal pipeline to agricultural sites, sports venues, industrial facilities and through one of San Antonio’s main tourist attractions, the River Walk, a three-mile long stretch of the San Antonio River developed for strolling, shopping, dining, and relaxing. San Antonio has avoided discovering the consequences of the River Walk running dry during the current years-long drought thanks to 468 acre feet per month of recycled water pumped into the stream. Recycled water also creates an attractive savings opportunity for businesses—recycled water rates are at least 84 percent lower than potable water rates for industrial uses.

Despite the cost, supply and byproduct advantages of recycled water, Porter cautioned that recycling too much of a region’s water supply can have negative ecological consequences. “Water recycling takes water out of the natural water cycle. If San Antonio recycles all the water that it takes in from other sources, it will cut down on river flow and spring flow. If we cut back on the rate of treated effluent, that creates a new problem,” he explained.

Funding: The Perennial Question
SAWS funds its projects with assistance from the Texas Water Development Board, which provides loans for water resource development at below-market interest rates. San Antonio plans to repay these loans using the SAWS Water Supply Fee. The variable-rate fee on water use ranges from 0.1223 cents to 0.4735 cents per gallon depending on customer type and monthly usage amounts. Residential and agricultural customer rates vary by usage, motivating residents and farmers to conserve in addition to raising money for supply expansion projects. All other SAWS customers must pay a flat water supply fee of 0.188 cents per gallon. 

After 2030

SAWS has not released detailed water management plans for the years following 2026. Its most recent long-term planning document, the 2012 Water Management Plan, states that expanded brackish water filtration, wider regional cooperation and, eventually, ocean water desalination provide the next opportunities for SAWS to expand its water supply.


Travis Hobbs is a freelance writer who reports on technical issues in international development, the nonprofit sector, and other interesting things that people ask him to research. He spends most of his time in Washington, DC and Austin, Texas.