The lower pH slows the growth of microbes that can slow or stop flowers from taking up water because they block the water conducting tissues of the flower stem. Flowers that quit taking up water have shorter vase lives. Citric acid is a safe organic acid that can be added to the water to acidify it. F. Warm water contains fewer dissolved gases than cool water. The dissolved gas bubbles can cause blockages in the water conducting tissues in the flower stem just like microbes.
Flowers also take up warm water better.
Unless water is pure, it will contain dissolved mineral salts. These affect the pH of the water and contribute to the hardness and alkalinity of the water. A low soluble salt content is best. Soluble salts can interfere with water uptake and cause burning on the tips of leaves and flowers. They also can interfere with the effectiveness of a floral preservative s ability to lower the pH of the water.