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Hard Water The presence of excess calcium (Ca) and/or magnesium (Mg) mineral ions in water results in the water being referred to as hard water. Calcium and magnesium minerals generally are measured in grains of hardness per gallons of water (GPG), parts per million (ppm), or milligrams per liter (mg/L). Soft water has a hardness of 3.5 GPG (60 ppm/60 mg/L) or less. Hard water has a hardness of 7 GPG (121 ppm/121 mg/L) or more. Softened water is any water that is treated to reduce hardness. Water hardness can be tested by independent water testing laboratories and some governmental health departments. Most public community water systems record the hardness of the water they supply. Mineral ions in hard water react with metal components and chemical agents, which causes two main problems in plumbing systems: scale, a hard, crusty deposit visible on taps, shower fittings, toilets, and water-using appliances (e.g., boilers, water heaters), which clogs pipes, fixtures, and appliances, reducing equipment efficiency and increasing energy costs; and, scum, which reduces the cleaning effectiveness of deter gents used for laundry, dish washing, and bathing. Water Softeners Water softening is a process that reduces or removes calcium and magnesium ions from hard water. There are many processes used in to soften water. The most used softening methods in residential installations are ion exchange and re verse osmosis. They are introduced in the sections that follow. The industrial methods used are very complex and include electrodialysis reversal (EDR), flashpoint distillation, thin film evaporation, and lime-soda ash softening. Ion-Exchange Water Softener An ion-exchange water softener operates by passing hard water through porous resin beads that have soft sodium/potassium ions attached to them. The ions contributing to hardness are re placed or exchanged with other ions that don’t contribute to hardness, thereby softening the water. After softening a large quantity of hard water the beads become saturated with calcium and magnesium ions. The resin beads then need to be regenerated by flushing a brine solution (salt-water mix) through the beads. The sodium ions in the brine recharge the beads so they will again be able to exchange the hard ions for the soft ions. Frequency of regeneration depends on the hardness of the water, the amount of water used, the size of the softener, and the capacity of resins to remove hardness. It’s done manually, automatically with a timer, or founded on a demand-initiated control based on quantity of water used. (See fgr.24.) The ion-exchange softening process adds sodium (salt) to the water, which could be troublesome for individuals on sodium restricted diets. Reverse Osmosis Water Softener A reverse osmosis water softener works by forcing water under pressure against a semipermeable membrane, where water molecules form a barrier that allows other water molecules to pass through while excluding most suspended and dissolved materials, including ions contributing to hardness. It’s called "reverse osmosis" because mechanical pressure is used to force water flow in a direction that is the reverse of natural osmosis (e.g., from a dilute to a concentrated solution). These softeners typically incorporate an activated carbon filter, which can provide added treatment for the volatile organic compounds (VOCs) not treated by the membrane itself. As a result, they are often called "water treatment devices." In residential applications, maintenance of a reverse osmosis softener involves the replacement of a membrane cartridge every two or three years, and replacement of the carbon filter cartridges once or twice per year. FGR.24 The layout of an ion-exchange water softener. FGR.25 An example of a load analysis worksheet for domestic water computations. Prev: PUMPS |