Hardness in water is usually observed by its ability to form scale and make suds with soaps and detergents. If your water leaves deposits in sinks and tubs, then it is moderately hard to hard. If you get lots of suds with soap, then the water is soft. Water hardness varies across the country and around the world.

Characteristics- Hardness in water is defined as the sum of the calcium and magnesium concentrations, expressed as calcium carbonate. The hardness of the water varies with the amounts of these salts. It is no longer an issue with laundry since most modern detergents contain water softeners.

Origin- The earth's terrain is rich in mineral content. Subterranean and surface waters absorb some of these minerals. Absorbed minerals include compounds of calcium and magnesium carbonates, bicarbonates, sulfates and chlorides. These naturally occurring minerals give water its hardness.

Measurement- Hardness in water is expressed in grains per gallon (g/g) or milligrams per liter (mg/L). To convert mg/L to g/g, divide mg/L by 17.1.

Denver's system has two distinct sources of water: The Moffat Collection System and the South Platte Collection System.

The Moffat Collection System
This source receives water from the Williams Fork Diversion System, the Fraser River Diversion System, and the South Boulder Diversion Intake Dam. Gross and Ralston reservoirs collect the water, which is treated at Denver's Moffat Treatment Plant. Primarily runoff from melting snow, it is soft, fluctuating seaonally between 2 and 4 grains per gallon.

The South Platte Collection System
Dillon, Antero, Eleven Mile Canyon, Cheesman and Platte Canyon reservoirs and the South Platte River make up the South Platte System. The water is collected in Strontia Springs and Marston reservoirs and treated at Denver;s Foothills and Marston treatment plants. This water is moderately hard because the South Platte River picks up minerals as it flows through the mountains. Depending on the season, hardness fluctuates between 5 and 7 grains per gallon.

Our water is slightly harder in the winter, when many lakes and streams freeze. It is softer during late spring through fall, when the snow melts and causes runoff that makes its way into the reservoirs.

Generally, people who live in the northern metro areas receive water from the Moffat System, which has softer water. People who live in the southern metro area usually receive water from the Foothills or Marston treatments plants. All customers might receive water from any plant or and blend of water from all the treatment plants. It takes detective work to figure out which source of water any of us getting at any given time. Denver Water routes and combines water throughout the city to meet customer demands.

Taste- very hard water can leave a chalky or mineral aftertaste. Water that is too soft leaves a flat, unpleasant taste. A balance needs to be maintained. Hardness versus softness are not health concerns, but aesthetic ones. Our goal is not only to maintain a safe product, but also one that tastes, smells, and looks good.

Scale- Denver's water tends to form scale. An initial scale usually takes two to five years to form and continues to build up over time. In older areas, while thick scale reduces rate of flow, it prevents water from being in contact with the plumbing. This protects pipes from corrosion and customers from potentially harmful metals. When using a cold water humidifier, hardness in the water can cause residue deposits on furniture. Deposits can be minimized by using half tap water and half distilled water in the humidifier.