Where Does Las Cruces Get Its Water? Aquifers and the Rio Grande

Las Cruces gets its water almost entirely from groundwater, pumping roughly 10 billion gallons a year from deep wells tapping two underground basins beneath and around the city.¹ A small annual allotment of Rio Grande surface water supplements that supply, but the aquifers do the heavy lifting. In a desert city averaging about nine inches of rain a year, where that water comes from, and how long it will last, is worth understanding.

The Two Aquifers Under the City

The city draws from two large underground basins, called bolsons: the Mesilla Bolson and the Jornada del Muerto Bolson.¹

The Mesilla Bolson runs along the Rio Grande on the west side of the city and gets some natural recharge from the river. The Jornada del Muerto Bolson sits to the east and is far more isolated. Its only meaningful recharge is rainfall and runoff filtering down from the surrounding mountains, which in this climate means the water replenishes slowly.

How the City Pulls It Up

Las Cruces Utilities operates 28 active wells inside or near the city limits. They draw from 300 to 1,000 feet down, deep enough to shield the supply from surface contamination and give it some cushion against short-term drought.¹

Water that has been sitting in rock for centuries picks up minerals on the way. Las Cruces groundwater carries moderate levels of calcium, manganese, and iron, which is why residents often see white deposits on fixtures and notice a mineral taste at the tap. That hardness is an aesthetic issue, not a health one.

The Rio Grande Share

The city holds an annual allotment of roughly 1,500 acre-feet of surface water from the Elephant Butte Irrigation District, which manages deliveries from the Rio Grande Project upstream.² An acre-foot is about 326,000 gallons, so on paper that is nearly half a billion gallons a year. In practice, much of it has gone to agricultural irrigation rather than straight to residential taps.

The city and EBID have launched a pilot study to use some of that surface water to recharge the Mesilla Bolson. Instead of letting the water evaporate or move downstream, the idea is to push it back into the ground where city wells can pump it later.²

Is the Water Safe to Drink?

Las Cruces reported no drinking water quality violations in its most recent Consumer Confidence Report, and the system consistently meets federal standards.¹ Arsenic, a common concern for Southwest groundwater, was detected at 3 parts per billion across the system. The federal maximum is 10 parts per billion.

PFAS contamination appears minimal so far. Sampling by the U.S. Geological Survey found no PFAS detections at one tested municipal well and only a trace-level estimated detection of one PFAS compound (PFPeA) at another, below the laboratory’s reporting limit.³ That sampling dates to 2020, and ongoing monitoring will matter as federal PFAS standards tighten.

Can the Supply Keep Up?

The underlying question is whether these aquifers can support a growing city in a region that gets so little rain. The city’s 40-Year Water Development Plan projects demand could reach roughly 44,000 acre-feet per year by 2055 under high-growth conditions, about double the 22,000 acre-feet used in 2015.⁴

Heavy pumping through the late 1980s drew down water levels in parts of the Mesilla Bolson, though observations since then suggest levels have stabilized in some areas. The Jornada del Muerto Bolson is the greater concern. Cut off from the Rio Grande and dependent on sparse mountain runoff, it does not bounce back quickly once it is drawn down.

The 40-year plan identifies several backup strategies if existing wells cannot keep up:

Aquifer storage and recovery, injecting treated reclaimed water from the East Mesa reclamation facility back underground for later use.
Importing groundwater by pipeline from more distant basins such as the Corralitos, Mimbres, or Salt Basin.
Drilling deep brackish-water wells more than 2,500 feet down and running the mineral-heavy water through desalination.

None of these are cheap or quick, which is why conservation is treated as part of the supply itself.⁴

What This Means for Your Household

Because the supply is finite and slow to refill, Las Cruces enforces a year-round Water Conservation Ordinance that regulates outdoor watering on an alternating schedule:⁵

Mondays: no outdoor watering for anyone.
Tuesdays, Thursdays, and Saturdays: even-numbered addresses.
Wednesdays, Fridays, and Sundays: odd-numbered addresses.

From April 1 through September 30, outdoor watering is restricted to before 10 a.m. and after 6 p.m. to cut evaporation during the hottest part of the day. Not repairing a known water leak within five working days also counts as water waste under the ordinance.⁶ The city’s long-range goal is to bring per-person water use down to 140 gallons per day by 2055, from about 181 gallons per day in 2015.⁴

1
Las Cruces Utilities. 2021 Las Cruces Utilities Consumer Confidence Report
2
City of Las Cruces. City, Irrigation District Partner in Groundwater Recharge Study
3
New Mexico Environment Department. USGS PFAS Sampling Results – Groundwater
4
City of Las Cruces. City of Las Cruces 40-Year Water Development Plan
5
City of Las Cruces. Water Conservation Program
6
City of Las Cruces. Water Conservation Regulations