Many garden experts recommend soaking seeds in distilled or purified water to avoid subjecting seeds to harmful substances that might be present in tap water. Some disagree and suggest that tap water is best because it has healthy minerals, such as calcium, that improve nutrition content in crops. Compared with saline water, distilled water helps seeds germinate quicker.
Distilling water has long been relied upon as a method of purifying water. Water is boiled and the resulting steam is condensed into pure water, making it free of many naturally-occurring minerals or other impurities. Like purified or filtered water, distilled water offers consistent content. It is free of chemicals and salt that would otherwise harm germination and is often recommended by agricultural experts for soaking seeds before germination. Compared with germinating in tap water, results tend to be more consistent with distilled water, which allows for predictable germination.
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Distilled Versus Tap Water
Tap water contents are often unknown, but they are likely to provide certain minerals necessary for plant nutrition. Tap water contains calcium, sodium, fluoride and chlorine in varying levels. Since some of these substances can be harmful to seeds, particularly sodium and chlorine, high levels could harm germination. But calcium levels in tap water actually improve nutrition levels in plants.
A Beijing study reported by the Withlacoochee Permaculture Guild reveals that mung beans and soybeans grown in tap water containing calcium and magnesium had higher levels of calcium once harvested. The beans, therefore, contained more healthy minerals for the human diet. In another study published by "Plant Food for Human Nutrition" in 1990, essential amino acid (protein) content in soybeans was higher when germinated in tap water versus distilled water.
Distilled Versus Saline Water
Many studies demonstrate that distilled water helps plants grow better than those germinated in saline water, because the sodium damages seed germination. High levels of sodium make it difficult for plants to conserve moisture properly, making them susceptible to drying up. In a 2002 University of Karachi study, seeds of a salt marsh perennial had difficult germinating in saline or seawater. But when placed in distilled water, the ungerminated seeds quickly grew, indicating that even salt-tolerant species germinated better in purified water.
Improving Germination Rates
For consistent germination results, soak seeds in distilled purified water before placing them in germination soil. To improve nutrient or mineral levels in crops, tap water may be best. Soil should be airy and light to allow seeds to penetrate. If starting seeds indoors, place the seedling tray or pot in a location that provides ideal germination temperature range, which varies among types of plants. Provide consistent moisture but do not oversoak the seeds while they germinate.