Hardness Test Kits

EDTA Method (Total)

The EDTA titrant is employed in alkaline solution with a calmagite indicator. This method determines the combined calcium and magnesium concentration of a sample. If no magnesium is present, the end point of the titration normally appears sluggish. Results are expressed as ppm (mg/l) CaCO₃.

References:
APHA Standard Methods, 22^nd ed., Method 2340 C- 1997.
USEPA Methods for Chemical Analysis of Water and Wastes, Method 130.2 (1983).

Technical Data Sheet

EGTA Method (Calcium)

The EGTA method is specific for calcium hardness. The EGTA titrant in alkaline solution is employed with a zincon indicator. Results are expressed as ppm (mg/l) CaCO₃.

Shelf Life: twelve months. Although the reagent itself is stable, the end point indicator has a limited shelf life. We recommend stocking quantities accordingly.

Reference:
West, T. S., DSC, Ph.D., Complexometry with EDTA and Related Reagents, 3^rd ed., pp. 46, 164 (1969).

Technical Data Sheet

Applications

Hard water is not used in industrial boiler installations or in the power generation industries because mineral deposits or scaling result in reduced boiler heat transfer efficiency, decreasing overall system performance and increasing energy consumption. Scaling can also block pipes, requiring pipe replacement, and cause corrosion. Water softening systems are therefore used for pre-treatment of boiler water. Regular testing of total hardness levels in boiler water is therefore important to ensure the correct amount of softening has been performed to ensure system performance and longevity. Target hardness levels are in the order of 0.3 ppm as CaCO₃ or less depending on drum pressure.

High hardness levels will impact the taste of drinking water. However, water hardness does not pose a health concern. Hard water will cause scaling of heat exchangers in domestic boilers and diminish the effectiveness of detergents and soaps used in washing machines, dishwashers and bathrooms, requiring more detergent or soap to produce a lather. Domestic water softeners are therefore sometimes used for these applications in areas of high hardness. Limescale may coat the heating element in kettles and irons, for example, making them less efficient, and deionised water is generally recommended for irons. Water softening adds additional cost and increases sodium levels which may not be desirable for drinking water, although as UK Drinking Water Inspectorate (DWI) maximum permitted sodium level is 200 ppm, then softened water may not exceed this (250 ppm CaCO₃ fully exchanged would result in 200 ppm Na⁺). Water companies do not soften potable water supplies as it is not cost effective. Total hardness variations according to geographic area are monitored and declared to the public. Total hardness is also commonly measured in communities that use groundwater wells as their primary water source.

What is Hardness?

Calcium and magnesium are the most common minerals that contribute to the hardness of water. Hardness is a measure of the mineral content of water and is dependent on the local geology. The greater the concentration of dissolved minerals, the ‘harder’ the water. Hardness is related to alkalinity as both measure CaCO₃ content. However, hardness is also a measurement of other dissolved metals that do not necessarily neutralise acidity. Naturally soft water has less alkalinity and is usually more acidic and may leach minerals and contaminants from piping.

Hard water causes scaling or mineral deposits to form on surfaces it comes into contact with, especially when heated. Temporary hardness is defined as the level of hardness in water resulting from Mg or Ca carbonate and bicarbonate that can be precipitated out of solution by boiling. Hardness can also interfere with the ability of soap and detergents to lather, on account of the strong positive charge of calcium (and Magnesium) ions in the hard water that bond with the negatively charged carboxylate hydrophilic (foam forming) part of the soap molecules, forming a precipitate. Water softeners exchange Ca²+ and Mg+ ions for Na+ ions on the resin beads and produce softened water.

The DWI categorises total hardness in the following manner.