Advice
Water softening and acidifying
Most domestic water supplies contain calcium and magnesium. Even where natural water sources are soft, water companies often add calcium to improve drinking quality. Hard water is unsuitable for ericaceous plants.
Professional growers treat hard water with concentrated acid but this option is not available to the gardener. However, reverse osmosis units that remove calcium and other impurities from tap water are available. Distilled or de-ionised water does not contribute towards alkalinity but is expensive to buy and prolonged use may lead to nutrient deficiencies. Rain water has an acid reaction and is suitable for watering all garden plants. Given sufficient storage capacity rainwater can be used for watering for much of the year.
Treated water from domestic softening units remains alkaline and elevated sodium levels will be present. Plants, especially seedlings and bedding plants, are sensitive to sodium chloride and prolonged use is not recommended. The use of water high in sodium may also destroy the structure of clay soils.