“Lawns don’t waste water, people do” (or “Lawns don’t waste water, people waste water”) is a slogan to encourage water conservation. “Landscaping doesn’t waste water, people do!” was cited in print in 1990, “Turf doesn’t waste water, people do” was cited in 1992, and “Lawns don’t waste water, people do” was cited in print in 1996.
 
“Lawns don’t waste water, people waste water” is a slogan similar in formation to “Guns don’t kill people, people kill people” (first cited in print in 1959).
 
   
23 November 1990, Mountain Democrat (Placerville, CA), “Answers to water management questions,” Pg. A-14, col. 1:
Q: Doesn’t landscaping waste water?
A: Landscaping doesn’t waste water, people do! Most landscapes are overwatered by 25 to 60 percent.
 
4 September 1992, Dallas (TX) Morning News, “Quality Landscaping: That’s what a xeriscape is all about” by Martha Sheridan,:
“Turf doesn’t waste water, people do,’ says Doug Welsh, one of the authors of Xeriscape Gardening: Water Conservation for the American Landscape (Macmillan, $30).
   
17 July 1996, MidCounty Chronicle (Port Neches, TX), pg. 11A, col. 2:
Lawns don’t waste water, people do
By BRUCB ACKBB
County Extension Agent, Agriculture
 
12 June 1998, The Gazette (Colorado Springs, CO), “LAWN/You may actually want some bluegrass,” pg. LIFE2, col.6:
“People who don’t care about what they are doing will need more water to have a ‘green’ lawn. Remember, plants don’t waste water; people do.”
 
30 September 2001, Salt Lake Tribune (Salt Lake City, UT), “Plants Don’t Waste Water, People Do” by Hilary Groutage Smith, pg. F5:
In the middle of a drought cycle and our unseasonably hot autumn, a coalition of landscapers, educators, gardeners and nursery owners made a recent statement to Utahns: Plants don’t waste water, people do.
 
4 May 2003, Los Angeles (CA) Times, “Whither the Lawn; What Southern California’s Booming Population and Looming Water Crisis Mean for the Great Green Carpet of Suburbia” by Preston Lerner, Magazine, pg. 14:
In other words, lawns don’t waste water; people waste water.
   
Google Books
Doug Welsh’s Texas Garden Almanac
By Douglas F. Welsh
College Station, TX: Texas A & M University Press
2007
Pg. 253:
Lawns don’t waste water; people do! Major universities have spent decades breeding turfgrasses for lawn use. Not a single one has bred a turfgrass that can reach up and turn on the water faucet.
   
Deseret News (Salt Lake City, UT)
About Utah: ‘Plants don’t waste water, people do’
By Lee Benson, Deseret News
Published: Wednesday, April 11 2007 9:14 a.m. MDT
The professional grass growers in Utah want to let you in on a little secret:
 
They use half as much water as you do.
     
Twitter
Stack Rock Group
‏@StackRockGroup  
Plants don’t waste water. People waste water.
12:29 PM - 1 May 13
 
The Eagle (Bryan-College Station, TX)
Do you know how much water your lawn needs?
Posted: Friday, June 21, 2013 12:00 am |  Updated: 8:20 am, Fri Jun 21, 2013. 
By Ben Wherley Special to The Eagle
There’s an old saying, “Lawns don’t waste water, people waste water.” As summer approaches in the Brazos Valley, spring rains will inevitably give way to hot and dry conditions. This is the time of year when many lawns take a turn for the worse. It’s during these stressful summer months that irrigation is often needed to supplement the scant amounts of rainfall we receive.