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A water’s “hardness” is derived largely from contact with soil and rock formations. Hardness is a measure of the levels of metal ions, mainly calcium and magnesium in the form of carbonates, in water.  While it is not generally dangerous to safety or health, water with excessive hardness can cause scale formation on fixtures and water heating elements and can reduce how well soaps lather.  Conversely, “soft” water can be corrosive, eroding pipe or other materials it comes into contact with.  Some utilities adjust the hardness of their water to achieve a level that will neither deposit scale nor be too corrosive.

The Acton Water District is fortunate in that most of our wells have a moderate amount of hardness. We often receive questions about how many “grains” of hardness our water has, as homeowners encounter this unit of measurement in manuals for dishwashers, fish tank filtering systems, etc.  While this unit of measurement is not commonly used in the U.S., it can easily be calculated from mg/L, the unit generally used to measure hardness here.  Approximately 17 mg/L of hardness equals one grain per gallon.  Raw water hardness from our wells varies, but an average of 65 mg/L could be used as a “ballpark.”


65 mg/L in our water equates to 3.82 grains/gallon



Water from the District’s wells falls on the higher end of the “soft” to the lower end of the “moderately hard” categories of hardness according to the U.S. Geologic Survey (USGS).  Customers should be assured that they will not experience the common problems attributed to very “hard” or very “soft” water. The most recent results for treated water entering our distribution system are listed in the table below.

Date  Source  Concentration (mg/L)
07/24/2023 Central Acton WTP 52
04/26/2023 North Acton WTP 61
02/21/2023 South Acton WTP 80