San Marcos could run out of water by 2047 if it doesn't act soon, according to the city's utility.
Population projections show the city will have about 303,000 residents by 2070; the city had planned for about half that number.
"So your [water] usage then goes from nearly 19 million gallons a day to over 33 million gallons a day," Tyler Hjorth, director of SMTX Utilities, said in a presentation this week to City Council.
Hjorth showed the Texas Water Development Board underestimated how many people would move to the region and how much water the city would need to keep up.
Paul Kite, assistant director of SMTX Utilities, said all these newcomers will strain the city’s water sources if the city does nothing.

San Marcos currently gets most of its water from the Edwards Aquifer and Canyon Lake. Recently, the city made a deal with Kyle, Buda and the Canyon Regional Water Authority to connect to the Carrizo-Wilcox Aquifer. A new water treatment plant connected to the aquifer opened in December. San Marcos could get water from it as soon as this year, once construction on the pipelines to Hays County is complete.
One way to address the growing demand is to get more water from the Carrizo-Wilcox Aquifer, Kite said. Another option is to focus on water conservation.
“ What we try to focus on more than anything else is educating folks,” Jan De La Cruz, conservation coordinator for the city, said. “We have a lot of people moving in from out of state and they're not used to water issues; they don't understand or know that there are restrictions.”
San Marcos is currently under Stage 3 drought restrictions, and residents are being told to conserve and limit water use outdoors.
De La Cruz said the city occasionally imposes fines on repeat offenders. But one of the city's main education campaigns is showing residents that saving water means saving money.
“The more water people use, the higher their water bills are going to be,” she said. “They go hand in hand.”
Hjorth said the city will explore expanding conservation methods, like its water rebate programs, and expanding its recycled water programs as part of its 50-year plan submitted and approved by the state.
De La Cruz said even if more water gets added to the city’s supply, conservation will be a priority.
”Conservation will definitely continue to be a key component of any of our water supply plans because conservation is the cheapest supply,” she said.