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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. 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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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:
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
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.
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:
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:
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  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.
There are three conceptual data points you might want to test:
Continue reading at SCALE PREVENTION, WATER HEATER or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: how to use the Taylor R-0012 water hardness test kit
How do I test for water hardness using Taylor R-0012 - 0.75 oz bottle? - Jim 7/27/2012
Jim the Taylor R-0012 -0.75oz bottle method for testing water hardness uses a combination of a bottle with a fill-level marking (0.75 oz) and a bottle of liquid reagent. The reagent is added to the test bottle and you watch for a color change. The number of drops to obtain the final color change translates into degree of hardness according to instructions packed with the reagent and kit.
In the article above on testing water hardness we have added more water test details from Taylor. Taylor explains that each test kit comes with detailed instructions.
Unfortunately the Taylor company's website when we last visited (July 2012) was challenging: we found it impossible to access the documents that were listed in some drop down menus. Better to contact the company directly 800-TEST KIT (837-8548), with your questions.
Questions & answers or comments about how to measure the hardness or mineral content of water
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