San Antonio's water is notoriously hard, but just how hard is it? In this definitive guide, we explain what water hardness means, how it is measured, and provide the specific hardness data for San Antonio and the surrounding Hill Country communities.
What is Water Hardness?
Water hardness is a measure of the dissolved mineral content in your water, primarily calcium and magnesium. These minerals are picked up as water flows through underground rock formations like the limestone that makes up the Edwards Aquifer. Water hardness is measured in Grains Per Gallon (GPG) or milligrams per liter (mg/L). The USGS classifies water hardness as follows: 0-3.5 GPG is soft, 3.5-7 GPG is moderately hard, 7-10.5 GPG is hard, and anything above 10.5 GPG is very hard.
San Antonio's Water Hardness: The Numbers
San Antonio's municipal water supply, sourced primarily from the Edwards Aquifer, averages approximately 21 Grains Per Gallon (GPG), or about 360 milligrams per liter. This places San Antonio's water firmly in the 'very hard' category — in fact, it is roughly double the threshold for 'very hard' water. To put it in perspective, San Antonio's water is among the hardest of any major city in the United States.
Water Hardness by Area
Water hardness varies across the San Antonio metro area and Hill Country depending on the water source. Here is a breakdown of approximate hardness levels by area:
- ●San Antonio (SAWS): 21 GPG — sourced from Edwards Aquifer
- ●Boerne: 15-18 GPG — mix of city water and wells
- ●New Braunfels: 15-21 GPG — varies by neighborhood
- ●Canyon Lake area: 20-30+ GPG — primarily private wells
- ●Spring Branch / Bulverde: 15-25+ GPG — mostly well water
- ●Kerrville: 12-18 GPG — Guadalupe River and wells
- ●Fredericksburg: 15-22 GPG — primarily well water
The Effects of 21 GPG Water on Your Home
Living with 21 GPG water without treatment means dealing with constant scale buildup on fixtures, shower doors, and inside pipes. Water heaters accumulate scale rapidly, reducing efficiency by up to 25% according to a Battelle Institute study. Dishwashers and washing machines have shorter lifespans. Soap and shampoo do not lather properly, leading to higher product usage. And the mineral deposits leave spots on everything from glasses to car paint.
The Solution: A Properly Sized Water Softener
The only effective solution for 21 GPG water is a properly sized and installed water softener. A water softener uses ion exchange to remove calcium and magnesium before the water enters your home's plumbing. For San Antonio's hardness level, we typically recommend a 48,000 to 64,000 grain capacity system for a family of 3-5 people. Proper sizing is critical — an undersized system will regenerate too frequently, wasting salt and water.