The mineral compositions of the water sources in Arizona vary depending on their origins (sources). In general, the chemical composition of groundwater sources is more seasonally constant but can vary significantly by location. The quality of surface water sources tends to vary both seasonally and by location.

Phoenix, and other surrounding cities such as Mesa and Gilbert, use multiple surface water sources including groundwater when necessary, that provide tap water with TDS values that exceed 500 mg/L (on average) and that can change more than +250 mg/L through the year. The combined hardness of these water sources is considered hard to very hard.

Tucson groundwater’s TDS is, on average, about 290 mg/L, but TDS values can vary by about +100 mg/L, depending on the location of the well in the Tucson basin. CAP water has a higher TDS than Tucson groundwater. Therefore, mineral concentrations in tap water are expected to increase as more CAP water is fed into the system. An estimate of the TDS and mineral composition of a 50-50 blend of Tucson groundwater and CAP water is about 450 mg/L. The combined hardness of this blend is classified as moderately hard to hard.

Flagstaff, on average, has about 200 mg/L TDS in its diverse (multiple surface and groundwater) sources, although values can change by more than +100 mg/L depending on the source. As in other Arizona cities, the hardness of Flagstaff city water ranges from moderately hard to very hard.

Yuma residents obtain their potable water directly from the Colorado River and it is not desalinized prior to delivery. At that location, the Colorado River has an average TDS of about 800 mg/L that changes about +50 mg/L through the year. The hardness of this source of water is classified as very hard.