Water hardness describes the concentration of dissolved alkaline earth metals in water, in particular calcium and magnesium. It is one of the most important parameters in water analysis and influences numerous applications in households, industry, agriculture and laboratories.
Depending on the concentration of these minerals, water is classified as soft, medium-hard or hard. Regularly determining the water hardness helps to assess the water quality and reliably monitor processes.
What is water hardness?
Water hardness is caused by dissolved calcium and magnesium ions that are absorbed when water comes into contact with rocks and soils. The concentration of these minerals can vary considerably depending on the region and water source.
Various units are used to describe water hardness, including
- Degree of German hardness (°dH)
- Millimoles per liter (mmol/L)
- Milligrams per liter (mg/L)
Water hardness provides important information about the composition of a water sample and is often determined as part of comprehensive water analyses.
Why is it important to measure water hardness?
Water hardness influences numerous technical and biological processes. It can have an impact on cleaning processes, water treatment, industrial applications and general water quality.
The water hardness is monitored in:
- Drinking water analyses
- Water treatment
- Industrial plants
- Laboratory applications
- Agriculture
- Aquaristics
- Research facilities
Regular monitoring helps to detect changes in the water composition at an early stage.
How is water hardness measured?
Water hardness is often determined using special test procedures or digital measurement methods. Modern measuring devices allow water samples to be analyzed quickly and reliably on site or in the laboratory.
The measurement results provide important information about the concentration of calcium and magnesium ions and support the assessment of water quality.
What factors influence water hardness?
Water hardness is determined by various natural influences.
These include in particular
- Geological composition of the subsoil
- Contact time of water with rocks
- Mineral content of the water source
- Groundwater and surface water shares
- Water treatment processes
The hardness values can vary significantly depending on the origin of the water.
Typical areas of application for water hardness measurement
Drinking water monitoring
The determination of water hardness provides important information about the composition of drinking water and is checked regularly.
Water treatment
In treatment plants, water hardness is an important parameter for monitoring and optimizing processes.
Industry
In technical systems, water hardness can have an influence on production processes and water quality.
Aquaristics and research
Monitoring water hardness also plays an important role in aquariums and scientific studies.
Water hardness measuring devices from Apera Instruments
Apera Instruments offers reliable solutions for determining water hardness for applications in water analysis, research and industry. The devices enable precise measurements and support the professional monitoring of water quality.
Frequently Asked Questions
What is the difference between hard and soft water?
Water hardness describes the concentration of dissolved calcium and magnesium ions. In Germany, according to the Detergent Act, soft water is defined as less than 8.4 °dH, medium-hard water as 8.4 to 14 °dH, and hard water as more than 14 °dH. Hard water causes limescale buildup, while soft water lathers better and is gentler on appliances.
In what units is water hardness measured?
The most common units are German degrees of hardness (°dH), French degrees of hardness (°fH), as well as mmol/l and mg/l CaCO3. In Germany, °dH is the standard unit. Internationally, mg/l CaCO₃ is frequently used. 1 °dH corresponds to 17.8 mg/l CaCO₃ or 0.178 mmol/l.
What is the optimal water hardness for an aquarium?
The optimal water hardness in an aquarium depends on the species of fish. Fish that prefer soft water, such as discus or neon tetras, prefer 2 to 8 °dH, while cichlids from the East African Rift Valley require 10 to 20 °dH. For most community aquariums, a range of 8 to 15 °dH is well suited.
Why is water hardness important for industrial systems?
Hard water causes limescale buildup in pipes, heat exchangers, boilers, and cooling systems. This reduces efficiency, increases energy consumption, and shortens the service life of the equipment. Regular water hardness measurements enable targeted water treatment and prevent costly damage.
What water hardness is recommended for agriculture and irrigation?
For irrigation in agriculture and horticulture, a water hardness of 5 to 15 °dH is recommended. Very hard water can raise the soil pH and impair the availability of nutrients to plants. In hydroponic systems, particularly soft water with a hardness of less than 5 °dH should be used to ensure precise adjustment of the nutrient solution.
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YD300 portable water hardness meter693.77 €
