You hear the term "hard water" constantly when living in Colorado, but what does it actually mean? Before you spend thousands on water treatment, it's important to understand the science behind water hardness.
What Causes Hard Water?
Water is an excellent solvent. As rain and snowmelt travel over and through the earth, they dissolve rocks and soils. "Hardness" simply refers to the amount of dissolved calcium and magnesium in the water.
In Colorado, water typically originates as pristine mountain snowmelt. However, as it flows down through the foothills, sits in reservoirs, or is pumped from underground aquifers (like the Denver Basin), it travels through limestone and chalk—picking up calcium carbonate and magnesium along the way.
How is Hardness Measured?
In the United States, water hardness is usually measured in one of two ways:
- GPG (Grains Per Gallon): The standard unit used by the water softening industry. One grain is equal to the weight of a single grain of wheat (about 64.8 milligrams).
- PPM (Parts Per Million) or mg/L: The scientific and municipal standard. You'll see this on Denver Water's quality reports.
The Conversion Formula
If your water report only shows PPM, use this formula to find GPG (which you need to size a softener):
Example: Denver's 133 PPM ÷ 17.1 = 7.8 GPG
The Hardness Scale
The Water Quality Association classifies hardness as follows:
| Classification | Grains Per Gallon (GPG) | Parts Per Million (PPM) | Status in Denver Metro |
|---|---|---|---|
| Soft | 0 - 3.5 | 0 - 60 | Rare (Only Boulder) |
| Moderate | 3.5 - 7.0 | 61 - 120 | Some Northern Suburbs |
| Hard | 7.0 - 10.5 | 121 - 180 | Denver Average (7.8) |
| Very Hard | 10.5+ | 180+ | Well Water, Brighton |
The Effects on Your Home
Calcium and magnesium are not health hazards—in fact, they are essential dietary minerals. The problem is what they do to your plumbing and daily life.
When hard water is heated or evaporates, it leaves the minerals behind in the form of a hard, rock-like crust known as scale. This causes:
- Plumbing Damage: Scale clogs pipes and ruins the heating elements in water heaters, significantly reducing their lifespan.
- Soap Inefficiency: Calcium reacts with soap to create a sticky "soap scum" rather than a lather, forcing you to use much more detergent.
- Skin & Hair Issues: That same soap scum sticks to your body, clogging pores and causing dry skin and brittle hair.
- Cleaning Headaches: Stubborn white spots on dishes, shower doors, and fixtures.