Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Soft or Hard Water

Carbonates dissolved in water.

Sponsored Links

"Hard water" is water containing a quantity of dissolved minerals. Water hardness is a function of the amount of dissolved calcium and magnesium salts, iron and aluminum.

Total hardness can be calculated as

Total hardness in ppm Carbonate  =

   2.497 ppm Calcium

    + 4.115 ppm Magnesium

    + 1.792 ppm Iron

    + 1.822 ppm Manganese

The salts occur in a variety of forms where typically calcium and magnesium bicarbonates are referred to as "temporary hardness", and sulfates and chlorides are referred to as "permanent hardness".

When hard water is heated the carbonates precipitate out of solution, forming scale on the heat surfaces.

Soap is less effective and prevented from lathering in hard water because its reacts to form calcium or magnesium salt from the organic acids of the soap.

"Soft water" is treated water where the only cation (the positively charged ion) is sodium.

Dissolved Calcium and Magnesium
Water Hardness Classification1)Milligrams per Liter
Grains per US Gallon
Soft 0 - 60 0 - 3.5
Moderate 61 - 120 3.5 - 7
Hard 121 - 180 7 - 10.5
Very Hard > 180 > 10.5

1) United States Geological Survey

  • 1 mg/L = 1 ppm
  • 1 ppm = 0.058 grains/US gallon
  • 1 ppm = 0.07 Clark degrees
  • 1 ppm = 0.1 French degrees

Hard water can be softened by passing it over an ion exchange resin.

  • zeolite processes for home water softeners
  • soda ash process for larger water softeners


Sponsored Links

Related Topics

Related Documents

Sponsored Links

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the SketchUp Pro Sketchup Extension Warehouse!

About the Engineering ToolBox!


We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.


This page can be cited as

  • Engineering ToolBox, (2005). Soft or Hard Water. [online] Available at: [Accessed Day Mo. Year].

Modify access date.

. .


3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Scientific Online Calculator

Scientific Calculator

3 10

Sponsored Links