Water hardness indicates the calcium and magnesium content in the water. This can form insoluble lime compounds. Water hardness is measured with the measuring unit “degree of German hardness” (dH). Rainwater is particularly soft water, which is especially suitable for laundry, because due to its excellent properties, it prevents scaling and wear on washing machines and only low detergent consumption is required. Rainwater is also advantageous for the growth of plants.