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Water - Hard Water vs. Soft Water

Just about everyone is familiar with the term "hard" water but few know what it really means.  In this blog I'll try to explain what "hard" water is and why we prefer water that is "soft."  In the blog It's Time To Talk About Water - Again, items 2 and 3 in the list of water contaminants refer to soft and hard water.  "Soft" water contains primarily readily soluble compounds while "hard" water contains compounds that are not readily dissolved in water.  "Hard" water creates the "lime" or "scale" deposits found in pipes.  Scale deposits not only reduce flow but also constitute a potential risk to equipment as particles of the hard water deposits are dislodged and enter the water supply.  Hard water also reacts with detergents and soap to cause a "scum" rather than bubbles.  This is similar to the soap scum found in residential bathtubs, wash basins and showers. Water hardness is measured in units called "grains per gallon" of dissolved solids or just "grains of hardness."  Calcium and Magnesium are the target minerals as these are the minerals common in water that form "insoluble" compounds. Interesting Note - A grain is a unit of weight which originated as the weight of a single grain of a cereal.  Although grain it is no longer widely used as a unit of measure, gunpowder is still commonly measured in grains and, historically, a dose of aspirin was frequently measured in grains.  The common aspirin dose was 5 grains which relates directly to today's single tablet dose of 325 milligrams. One grain equals 64.799 (call it 64.8) milligrams.  Doing the math, grains per gallon (gpg) converts to mg/liter by the equation -

milligrams per liter = grains per gallon times 17.1 1 grain of hardness = 17.1 milligrams per liter

Many instruments commonly used in cleaning systems measure contaminants dissolved in water in the units "parts per million" which is ratio of the weight of the dissolved insoluble (really partially soluble) contaminants to the weight of the water in which they are dissolved.  Parts per million (ppm) is the same as milligrams per liter since water weighs one gram per milliliter.  The measure parts per million is much more commonly used than grains per gallon.  It is important to know that they are both measuring the same thing but using different units. How Hard Is My Water? - Almost all water except for water that has been specifically treated to remove them contains dissolved minerals in some quantity.  In general, the following descriptions apply.
  • Soft Water = less than 1 grain per gallon (0 to 17 milligrams per liter or ppm)
  • Slightly Hard Water = 1 to 3.5 grains per gallon (17 to 60 mg/liter)
  • Moderately Hard Water = 3.5 to 7.0 grains per gallon (60 to 120 mg/liter)
  • Hard Water = 7.0 to 10.5 grains per gallon (120 to 180 mg/liter)
  • VERY Hard Water = greater than 10.5 grains per gallon (greater than 180 mg/liter)
Water from a municipal supply usually comes with a pedigree (of sorts) which is available from local authorities and should specify the hardness.  In fact, the water may already be treated to reduce certain minerals while others are added for public health and other reasons.  If your water supply is from a well or other private source, it is a good idea to have a water analysis done in the early stage of facility planning.  Water quality may have a significant impact on not only cleaning system design but the design of the overall facility as well. Fortunately, there are many ways to reduce and even totally eliminate water hardness.  Ways to reduce and eliminate hardness will be discussed in upcoming blogs.

-  FJF  -

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