Water hardness refers to the concentration of dissolved mineral ions, primarily calcium and magnesium, in a water supply. These minerals are naturally picked up as water flows through soil and rock, particularly in areas rich in limestone or gypsum. Understanding this level is the first step toward addressing potential issues like scale buildup in pipes and appliances. This article guides you through the methods available for determining water hardness.
Understanding Water Hardness
Water hardness is defined by the presence of multivalent cations, with calcium ions and magnesium ions being the major contributors. These dissolved metal ions react with soap to form an insoluble residue known as soap scum, which is a common indicator of hard water. The total hardness of water is the sum of two distinct types: temporary and permanent hardness.
Temporary hardness is caused by calcium and magnesium bicarbonates and can be removed simply by boiling the water. Heating causes the bicarbonates to precipitate out as solid calcium carbonate, often seen as limescale inside kettles and hot water heaters. Permanent hardness is due to calcium and magnesium sulfates and chlorides. Unlike temporary hardness, these compounds are not removed by boiling and require chemical treatment or a water softener for reduction.
Simple Home Tests for Initial Assessment
Before moving to precise quantitative measurements, a quick, qualitative assessment can be made using simple household items. The most accessible method is the “Soap Lather Test,” which relies on the reaction between soap and the dissolved minerals. In this test, a water sample is mixed with a small amount of pure liquid soap and shaken vigorously. Soft water will readily form a substantial, stable lather with only a small amount of soap.
If the water is hard, the calcium and magnesium ions react with the soap to form a cloudy, insoluble precipitate, or scum. This reaction makes it difficult for a stable foam to form, meaning a greater volume of soap solution is needed before a persistent lather is achieved. Another indicator is a visual inspection of appliances and fixtures. The presence of white, chalky scale buildup, particularly on showerheads, faucets, and inside kettles, suggests high water hardness. These initial observations provide an assessment of whether hardness is a problem but do not offer a numerical value.
Accurate Measurement Using Test Kits
To move beyond a simple assessment and obtain a precise numerical value, specialized home test kits are necessary. These kits fall into two main categories: test strips and liquid titration kits, each offering a different balance of speed and accuracy.
Test Strips
Test strips are the most common and easiest method for a quick, initial reading. The procedure involves dipping a disposable strip into a water sample for a specified short time, which causes the chemical pads on the strip to change color based on the total mineral concentration. The user then compares the resulting color of the strip to a provided color chart to estimate the water hardness level. Test strips are fast and straightforward, but their accuracy is limited by the user’s ability to precisely match the color and by the strip’s resolution. They are best used for a general understanding.
Liquid Titration Kits
For a more reliable measurement, a liquid titration kit, often called a drop test kit, is preferred. This method is considered the gold standard for home testing due to its accuracy. The titration procedure involves adding a specific volume of water sample to a container, followed by a buffer solution and a color indicator. A titrant solution, typically containing a chelating agent like EDTA, is then added drop by drop while the mixture is swirled. The endpoint of the test is reached when the solution undergoes a distinct color change, signaling that all the hardness ions have reacted with the titrant. The number of drops of titrant used directly correlates to the water’s hardness level, which is then calculated using the kit’s instructions.
Interpreting Results and Hardness Scales
Once a quantitative test is performed, results are typically expressed using one of two common units: Parts Per Million (PPM) or Grains Per Gallon (GPG). The PPM unit is equivalent to milligrams per liter (mg/L) and directly measures the concentration of calcium carbonate in the water. The GPG unit is a traditional measure often used in the United States, where one GPG equals 17.1 PPM.
These numerical results are categorized using a standard classification scale to determine the water’s quality. The United States Geological Survey (USGS) classification is widely used:
- 0 to 60 PPM (0 to 3.5 GPG) is considered soft.
- 61 to 120 PPM (3.5 to 7 GPG) is considered moderately hard.
- 121 to 180 PPM (7 to 10.5 GPG) is classified as hard.
- Above 180 PPM (10.5 GPG) is considered very hard.