Ensuring a Safe, Sustainable Future Water Supply

Case Study

Teresa Long

May 3, 2011

Introduction

By the year 2060, water usage in Texas will exceed the available water supply due to rapidly

increasing population growth. Existing sources of water supply are inadequate to sustain future

demands for farming, ranching, recreation, and the environment. An additional 8.5 million acre-

feet per year of new water supplies will be needed. Ensuring a sustainable water supply in a

semi-arid climate is challenging and exacerbated by unpredictable factors such as climate change

associated with global warming. How will stakeholders meet future demand?

Methodology

New technologies must be identified and developed to supply increased demand. This study

focuses on several innovative technologies in various stages of planning and implementation by

the Texas Water Development Board. This study also briefly examines technologies emerging in

other countries that will help ensure a safe, sustainable future water supply.

Meeting Future Demand

Ensuring a safe, sustainable water supply to meet the demand required for the projected

population for the year 2060 will entail development and implementation of many options.

Strategic water management practices which advocate using existing sources wisely, capturing

and storing water, and reusing wastewater must be implemented and followed. Innovative

technologies must be identified and developed. After suffering the most severe drought in the

history of Texas (1954-1956), the Texas Water Development Board (TWDB) was founded in

1957.

According to the TWDB, plans to meet the projected demand of 8.5 million acre-feet per year

of new water supplies necessary to keep up with expected population growth for 2060 include:

60 % -- Conventional water sources

24% -- Conservation

16 % -- Desalination, brackish groundwater desalination, reuse and reclamation,

rainwater harvesting, and aquifer storage and recovery

A single source will not be adequate to supply demand. We must develop a diverse combination

of technologies which includes desalination, brackish groundwater desalination, rainwater

harvesting, aquifer storage and recovery (ASR), reuse, and emerging technologies.

Desalination

Desalination is the process of removing dissolved salts from saline water to produce

freshwater. Texas has an infinite, drought proof-supply of seawater along its 370 miles of

coastline. Although Texas does not currently have a seawater desalination plant, optimization of

existing technology has decreased the cost associated with desalination, making it a cost-

effective alternative source of water.

Two processes are currently used, the thermal process and the membrane process. The

thermal process involves heating saline water to the boiling point, then condensing and collecting

the water vapor. Membrane processes such as reverse osmosis and electrodialysis separate salts

from water using a permeable membrane. Both processes generate toxic by-products (salts and

brine) which must be disposed of, adding to the cost of producing freshwater from saline water.

Brackish Groundwater Desalination

Seawater typically contains greater than 35,000 milligrams per liter of Total Dissolved Solids

(TDS). The higher the concentration of TDS, the more pressure required to push the water

through membranes, which increases the cost of production. Brackish groundwater contains a

significantly lower concentration of TDS, making it less costly to process than desalination of

seawater. Almost every aquifer in Texas contains brackish groundwater. Approximately 2.78

billion acre-feet are available for desalination. Currently, 38 brackish groundwater desalination

plants, many of which are small-scale facilities and pilot plants, are operational.

While past studies estimated volumes, they failed to assess groundwater quality. In 2009 a

program was funded and implemented to develop better tools to assess parameters, characterize

and map brackish groundwater aquifers, and develop flow models to determine aquifer

productivity.

Rainwater Harvesting

Rainwater harvesting is the forgotten practice of capturing, storing, and using rainwater. One

inch of rainfall that falls on a 2,000 square foot roof yields 1,000 gallons of harvestable water.

Average household systems can collect as much as 32,000 gallons per year even in a semi-arid

region. Rainwater collected is suitable for use in landscape irrigation, household use, and may

be suitable for drinking with minimum treatment. Large-scale systems are being developed by

municipalities.

Aquifer Storage and Recovery

During periods of heavy rain, appropriated surface water can be collected for subsequent

retrieval and injected, via well used for both injection and recovery, into a geologic formation

capable of underground storage (Class V aquifer). Stored water can be retrieved in dry or

drought years to help meet demand. Today, more than 75 ASR wells are operational in the

United States, compared to only three in 1968. Texas is lagging behind other states with only 67

Class V aquifers in use today. Feasibility studies using different water supply sources, in addition

to different types of aquifers, show the technology is viable but many regulatory and legal

barriers remain.

Reuse

Reuse and reclamation of wastewater is drought-proof and a key component in ensuring

future water supply. Texas is expected to nearly double its reuse capacity by 2060. Domestic or

municipal wastewater can be reclaimed and treated to a quality suitable for either direct or

indirect reuse. In direct reuse, effluent is piped directly from wastewater treatment plant to point

of use. Indirect reuse is when effluent re-enters a river, stream, or aquifer and is retrieved for

subsequent use at a different point in the system. Reclaimed water is commonly used for

industrial and power plant cooling water.

Reusing treated wastewater effluent from wastewater treatment plants after further treatment

at an integrated membrane facility in close proximity to industrial users, can supply industrial

users with water suitable for use as process and boiler water. Reuse of this water releases the

surface water for currently used for industry to meet other needs.

Emerging Technologies

The atmosphere contains 0.001% of the Earth’s total water reservoir volume of 350 million

cubic miles. Water-from-air technology converts the humidity in the atmosphere to liquid water

using refrigeration methods that cool the air below its “dew point” Site-specific designs for

tropical coastal sites with access to deep, cool ocean waters that are used as a coolant produce

freshwater from saline water without pumping salts back into the ocean. Solar powered

desalination units and solar powered atmospheric generation units are currently under

development. These processes do not require fossil fuel to operate, and do not produce toxic by-

products that require disposal. Units can be either small-scale or large-scale.

Conclusion

Identifying and developing new technologies, along with a strategic water management plan

that includes using existing sources wisely, is absolutely essential in ensuring a safe, sustainable

water supply. Humankind cannot continue to squander our most precious resource. Future

generations will ultimately suffer if our misuse continues unchecked. There is no substitute for

water.

Cited References

Texas Water Development Board [homepage on the Internet]. (TX): n.d. [cited 2011 Apr. 4].

Available from: http://www.twdb.state.tx.us.

Air Water Well [homepage on the Internet]. n.d. [cited 2011 Apr. 3]. Available from:

http://www.airwaterwell.com/.

Warair [homepage on the Internet]. n.d. [cited 2011 Apr. 3]. Available from:

http://www.watair.com.

DeSalWave [homepage on the Internet]. n.d. [cited 201 Apr. 4]. Available from:

http://www.desalwave.com/.

Texas Water Development Board (USA) Ship Channel Wastewater Reclamation and Reuse

Feasibility Study Final Report. Austin (TX): 2005 Oct.