Finch, Dr. Calvin

Texas A&M University

8 txH2O  Fall 2013
Column by Dr. Calvin Finch, Water Conservation and Technology Center director
WAT E R
CONSERVATION
& TECHNOLOGY
CENTER
Securing Our Water Future
graywater:  
an underused  
resource
Graywater is a “new” water resource that could 
provide a relatively quick, inexpensive and easy way 
to extend Texas water supplies. It is ready to use at 
our homes, where it is produced.
Graywater is water captured from the clothes 
washing machine, bathroom sink, shower and 
bathtub. According to the Uniform Plumbing Code, 
a typical household produces 100 gallons of usable 
graywater per day. Dr. Raul Cabrera of the Texas 
A&M AgriLife Research and Extension Center 
at Uvalde, in research funded by the Rio Grande 
Basin Initiative, has said that amount of water could 
replace 10 percent to 25 percent of the potable water 
used on a typical Texas landscape. 
My calculations show that a statewide push 
to retrofit 3.9 million homes to use 33 gallons of 
graywater a day would produce around 390,000 
acre-feet of water per year. That is an impressive 
amount of water. 
Another impressive number — an impressively 
low one — is the cost of retrofitting a home for 
graywater use as demonstrated at the Mitchell Lake 
Audubon Center in San Antonio. The common 
perception is that retrofitting a home for graywater 
is expensive. But at the center, Mike Martin of the 
Texas Center for Applied Technology in the Texas 
A&M Engineering Experiment Station (TEES) has 
shown that a homeowner could perform a retrofit 
for between $100 and $500. That is a small expense 
to supply 100 percent of the water needed for a 
low-water-use landscape or 15 percent of the water 
needed for a typical lawn. 
Despite a body of scientific evidence that says 
graywater is safe for landscape use, regulatory 
officials and the public still have questions 
about its safety. The Water Conservation and 
Technology Center and a team of TEES engineers 
and researchers are working on a graywater 
initiative to address these questions. They are 
reviewing available research and identifying gaps in 
confirming the safety of graywater use. In addition 
to filling gaps in the science, this team is working 
to enhance adoption by delivering timely, easy-to-
understand materials to the public, policy makers, 
city officials and others. The graywater initiative will 
need a major education component to be successful. 
For example, water purveyors have questions 
about how a large-scale graywater program will 
affect sanitary sewer operations and existing 
recycled water (treated wastewater) programs. 
Homeowners and regulators also want more 
information on graywater retrofit and irrigation 
application options. Considerable research already 
exists on plant and soil responses to graywater, but 
it needs to be reviewed, organized and presented 
in an easy-to-use format for consumers. Finally, 
further research is needed on how graywater, air- 
conditioner condensate and harvested rainwater can 
be used together.
The lack of knowledge and the perceived issues 
that exist with graywater use are reflected in 
the attitudes of many local regulators and in the 
ordinances that govern graywater use in their cities.
In 2003, Robert Puente, then state representative 
from Bexar County, authored HB 2661. The bill 
was designed to liberalize the use of graywater and 
exploit its full potential. Unfortunately, the intent of 
HB 2661 was never communicated to homeowners 
who might consider using the resource. It is unclear 
whether communities’ regulations are much more 
limiting than needed or whether reasonable regula-
tions are interpreted in ways that are not supportive 
of graywater use. The local ordinance and interpre-
tation situation is an important factor that needs 
addressing if graywater use is to reach its full 
potential.
The average cost to build a reservoir is about 
$500 per acre-foot, not including the first year the 
reservoir is online, which costs $1,000 per acre-foot.
If, as projected, a statewide graywater initiative 
could produce 390,000 acre-feet per year at an 
average of $300 per acre-foot, then it should be 
pursued. 


English

Graywater: an underused resource

Texas A&amp;M Repository

8 txH2O  Fall 2013Column by Dr. Calvin Finch, Water Conservation and Technology Center directorWAT E RCONSERVATION& TECHNOLOGYCENTERSecuring Our Water Futuregraywater:  an underused  resourceGraywater is a “new” water resource that could provide a relatively quick, inexpensive and easy way to extend Texas water supplies. It is ready to use at our homes, where it is produced.Graywater is water captured from the clothes washing machine, bathroom sink, shower and bathtub. According to the Uniform Plumbing Code, a typical household produces 100 gallons of usable graywater per day. Dr. Raul Cabrera of the Texas A&M AgriLife Research and Extension Center at Uvalde, in research funded by the Rio Grande Basin Initiative, has said that amount of water could replace 10 percent to 25 percent of the potable water used on a typical Texas landscape. My calculations show that a statewide push to retrofit 3.9 million homes to use 33 gallons of graywater a day would produce around 390,000 acre-feet of water per year. That is an impressive amount of water. Another impressive number — an impressively low one — is the cost of retrofitting a home for graywater use as demonstrated at the Mitchell Lake Audubon Center in San Antonio. The common perception is that retrofitting a home for graywater is expensive. But at the center, Mike Martin of the Texas Center for Applied Technology in the Texas A&M Engineering Experiment Station (TEES) has shown that a homeowner could perform a retrofit for between $100 and $500. That is a small expense to supply 100 percent of the water needed for a low-water-use landscape or 15 percent of the water needed for a typical lawn. Despite a body of scientific evidence that says graywater is safe for landscape use, regulatory officials and the public still have questions about its safety. The Water Conservation and Technology Center and a team of TEES engineers and researchers are working on a graywater initiative to address these questions. They are reviewing available research and identifying gaps in confirming the safety of graywater use. In addition to filling gaps in the science, this team is working to enhance adoption by delivering timely, easy-to-understand materials to the public, policy makers, city officials and others. The graywater initiative will need a major education component to be successful. For example, water purveyors have questions about how a large-scale graywater program will affect sanitary sewer operations and existing recycled water (treated wastewater) programs. Homeowners and regulators also want more information on graywater retrofit and irrigation application options. Considerable research already exists on plant and soil responses to graywater, but it needs to be reviewed, organized and presented in an easy-to-use format for consumers. Finally, further research is needed on how graywater, air- conditioner condensate and harvested rainwater can be used together.The lack of knowledge and the perceived issues that exist with graywater use are reflected in the attitudes of many local regulators and in the ordinances that govern graywater use in their cities.In 2003, Robert Puente, then state representative from Bexar County, authored HB 2661. The bill was designed to liberalize the use of graywater and exploit its full potential. Unfortunately, the intent of HB 2661 was never communicated to homeowners who might consider using the resource. It is unclear whether communities’ regulations are much more limiting than needed or whether reasonable regula-tions are interpreted in ways that are not supportive of graywater use. The local ordinance and interpre-tation situation is an important factor that needs addressing if graywater use is to reach its full potential.The average cost to build a reservoir is about $500 per acre-foot, not including the first year the reservoir is online, which costs $1,000 per acre-foot.If, as projected, a statewide graywater initiative could produce 390,000 acre-feet per year at an average of $300 per acre-foot, then it should be pursued. 

https://oaktrust.library.tamu.edu/bitstream/1969.1/150905/1/Calvin%20Column.pdf

Graywater: an underused resource

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Graywater: an underused resource

Abstract

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Full text

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Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository