Water hardness strip test (C) D FriedmanHow to Measure the Hardness Water
Water hardness test procedures & water mineral content tests

  • WATER HARDNESS: HOW TO MEASURE - CONTENTS: How is Water Hardness Measured? Table of water hardness data, measurements and numbers. What does "grains of hardness" mean? How to use a simple soap test to measure the grains of hardness of your water supply . Where to buy Water Test Kits & Guide to Using a Water Hardness Test Kit. Measuring Water Hardness to Test Water Softener / Water Conditioner Operation using Water Hardness Test Tablets. A survey of different methods & prices for water hardness testing and we include description of the different tests, their technology, and their application
  • POST a QUESTION or READ FAQs about how to measure the hardness or mineral content of water
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How to test water hardness & how to measure it using test strips, a water hardness soap test solution and other methods.

This article explains how to measure water hardness or grains of hardness: a measure of water mineral content. We provide a table of water hardness measurements and we discuss different methods for measuring water hardness including a simple soap test.

Electronic instruments can also measure water hardness but are a cost that most homeowners can eschew given the very low, even free costs of other water hardness test methods.

We give references on where to buy water low-cost but quite effective water hardness tests and we describe how various water hardness test kits are used and how to choose among them.

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How to Measure Water Hardness: how many grains of hardness is found in your water?

Lime scale fragments from a water heater (C) Daniel FriedmanDefinition of hard water

As we explain in more detail at WATER SOFTENERS & CONDITIONERS, Water "hardness" refers to the level of unwanted minerals, principally calcium and magnesium, found in your water supply.

Hard water is an aesthetic issue (poor lathering, spots on dishes) and a mechanical issue (clogged pipes, expensive repairs, poor washing machine performance) but it is not a health concern.

Photo at left: lime scale fragments collected from a water heater. [Click to enlarge any image]

Hard water is found only in certain neighborhoods and usually only on private water supplies from a local well or wells.

At DETECT HARD WATER we describe how to visually detect that your water is high in mineral content or "hard".

How is water hardness measured?

Water hardness is measured in "grains" per gallon, in milligrams of calcium (Ca) per liter, or water hardness may be expressed in ppm - parts per million, and also in German Degrees of Hardness (dH) [which we drop here as this is for fish tanks]. You can take a water sample to a water test lab to have its hardness measured, but it is also trivially easy to measure the hardness of water yourself, as we explain here.

Readers whose water is acidic or corrosive rather than "hard" and readers needing to know about the Langelier Saturation Index or LSI should see CORROSIVITY or ACIDITY of WATER.

How to convert among different water hardness measures:

Water with hardness of 25 ppm = 25 mg. of hardness-causing minerals per liter of water.

Table of Degrees of Water Hardness

Soft water 0-17.1 mg/L of minerals
Slightly hard water 16.1-60 mg/L of minerals
Moderately hard water 61-120 mg/L of minerals
Hard water 121-180 mg/L of minerals
Very hard water more than 180 mg/L of minerals

- adapted from web search Wikipedia 01/31/2011

You can compare the water hardness range above with the water hardness test sensitivity of the various water hardness tests listed later in this article.

We repeat this table with more details, below where we show other measures of water hardness..

Use this simple soap test to measure the grains of hardness of your water supply

You will need:

Water hardness can be easily measured using a simple soap test kit that will measure in "grains of hardness" (a little bottle with a line marked on it which you fill to the line with water, add a drop of soap, and shake to look for suds. More drops of soap - more degrees of hardness).

The very crude do-it-yourself water hardness test method that some folks try is just adding dish soap to 12-oz of tap water (the left two columns in our table below). In our OPINION this is a very crude test and you'd be better off obtaining a free or low-cost but more accurate water hardness test from one of the sources listed below at Water Test Kits & Guide

Water Hardness Measurements - How to Use the Home Soap Test Method for Water Hardness

Test Water Volume - crude test Soap drops - crude test Grains/gallon GPG of Water Hardness

ppm mg/L

Water hardness in parts per million in milligrams per liter

Softness of the Water
12 oz 10 0 - 1 0-17.1 Very Soft
  20 1 - 3.5 17.1 - 60 Slightly Hard
  30 3.5 07/13/2010 - 07.0 60 - 120 Medium Hard
  40 7.0 - 10.5 120 - 180 Hard
  50 10.5 & higher 180 & over Very Hard
NOTE: 1 German degree of hardness dH = 17.5 ppm. For fish tanks, 200-300 ppm is considered "hard", 300-500 ppm "very hard" and over 500 ppm "extremely hard" water.

Sources of Water Test Kits & Guide to Using a Water Hardness Test Kit

Water hardness test kit Water hardness test kits may use water hardness test tablets or paper test strips (see below).

When mixed with (a test tablet) or wet by (a test strip such as those shown at left) water of a specified volume (fill the test bottle with the specified amount dictated by the test kit instructions or to the line marked on the test bottle), the water in the bottle plus test tablet changes color (green or red, for example) or the test strip changes color (on a scale, for example) that is compared to a standard provided with the kit.

Other simple test kits provide a small glass bottle with a line marked on it and intended for use with dishwasher soap. One drop dish soap at a time. More soap drops = harder water.

We bought our Total Water Hardness Test Kit at Sears where water softeners were sold. Or the hardness of your water may be measured at no charge if you ask the local water treatment company to take a look.

A typical water hardness test kit that uses water strips provides with each strip a color chart. Match the color on the strip (after you wet it with your test water) against the color chart to see the hardness of your water sample, measured in ppm or gains. A typical water hardness test kit strip measures hardness from 0-1000 ppm or from 0-59 grains of hardness.

Potable Water Hardness Test Kits: sources, features, costs

Here we describe different methods & prices for building water supply hardness testing and we include description of the different tests, their technology, and their application. [These water tests are available at Amazon.com through links given here, from the companies and producers listed here, and from other suppliers]

Watch out: a general search for "water test kit" or "water hardness test kit" will list kits and tests that may not match your application. Don't order an aquarium test kit or a swimming pool test kit if your need is to test building drinking water or potable water supply. The test criteria, methods, and standards may be quite different.

[Disclosure: you can buy these test kits from many online sources including Amazon.com. Amazon pays us a pittance per item if purchased via these links. Here are our WEBSITE VISITOR PRIVACY POLICY (we do not collect any information about individual website visitors) and our ADVERTISING POLICY.]

What's the difference between using a total water hardness test strip kit and using the "true calcium" liquid reagent drop count titration method?

Water hardness or other water test kits are used in a very wide variety of applications beyond simply checking a drinking water supply. Some other uses include balancing the water hardness of pools and spas, testing the condensate in a steam boiler system or in water operated cooling towers, and checking the proper operation of water softeners.

A difference between this calcium test using the dropcount titration method and total hardness test kits that use a test strip is that the test strips only measure total water hardness - which is perfectly fine for examining a residential water supply. But for measuring water hardness when maintaining a pool or spa, you need to measure calcium hardness specifically. That measurement requires the drop count titration method described next. Quoting from Taylor who explains the difference in exquisite detail:

... whereas test strips for total hardness have just four or five color blocks to cover a tremendously wide range—from 0 to 1,000 parts per million (ppm) with color blocks for 0, 100, 250, 500, 1,000, for instance—a drop test will allow you to approach the true concentration of calcium hardness in 10-ppm increments. This means if you're faced with wanting to balance water in a spa by increasing the calcium hardness from 60 ppm to 150 ppm, the strip can't help but the drop test can.[9]

How to use the Taylor R-0012 water hardness test kit - drop count titration method

This water hardness test method uses a water hardness reagent, an organic chelant solution whose principal ingredient is Ethylenediaminetetra- 60-00-4 <5 Irritant acetic acid. The reagent is added drop by drop to a quantity of test water and the user looks for a permanent color change in the water test sample. By using the Taylor R-0012 0.75 oz test bottle and filling the bottle to a mark provided on that container you can be assured that you are using the proper test volume. In discussing water hardness testing (calcium level) in a discussion of pools and spas, Taylor adds these details:

The color progression in a hardness test is from red, to a mixture of red and blue, to blue. To be certain the color change is permanent, indicating you have reached the true endpoint, add one more drop of titrant. If the blue color remains unchanged, do not count this drop.[9]

Taylor also warns about water hardness tests (using a reagent and drop count titration) that produce a "fading endpoint" - the color ends at purple rather than blue due to contamination of the test water by metal ions. The company provides a procedure for adjusting the process if this happens during your test.

Store your reagent between 36-85 degF., keep it out of direct sunlight, and avoid abrupt temperature changes that can cause reagent deterioration. Handle appropriately. Like many acid reagents the liquid can be a skin or eye irritation. Taylor's website provides an MSDS if you need it. More information is available from the manufacturer, Taylor Technologies [9] whose contact information is at our references section below.

Measuring Water Hardness to Test Water Softener / Water Conditioner Operation using Water Hardness Test Tablets

If you need to confirm that your water softener equipment is working properly you will want to measure the hardness or mineral content of your water supply taken at a plumbing tap (sink faucet) located after or "downstream from" the water softener. The following procedure is adapted from IBC [using "water hardness tablets" and other water conditioner installation manuals.[8]

There are three conceptual data points you might want to test:

  1. incoming water hardness - take a water sample from a tap that bypasses or is before the water softener
  2. water hardness after a water softener regeneration or "backwash" cycle
  3. water hardness a day or more after a backwash cycle, or each day of normal water usage in the building between one backwash cycle and the next one - this can confirm that the settings on the water conditioner controls, including regeneration or backwash cycle frequency are adequate.

Electronic Instruments for Testing Water Hardness: Colorimeter, Ion Detector, other

Electronic instruments can also measure water hardness but are a cost that most homeowners can eschew given the very low, even free costs of other water hardness test methods. But since some fellows complained about feeling left out:

Watch out: there are some low cost but poor-functioning meters & test instruments we see for sale at auction and stores offering devices that may "work" but may not be suitable if accuracy is important.


Continue reading at SCALE PREVENTION, WATER HEATER or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

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