What makes water hard
As rainwater soaks through soil and rock, it picks up minerals. Where the ground has chalk, limestone or similar deposits, the water collects calcium and magnesium. This mineral content is what we call hardness. Much of India's groundwater is hard, which is why borewell supplies in many cities leave white marks on almost everything they touch.
Hard water is not unsafe to drink in normal circumstances. The trouble is what it does to equipment. When hard water is heated or left to dry, the calcium and magnesium come out of solution and stick to surfaces as a hard white layer called scale.
How hardness is measured
Hardness is usually reported as milligrams of calcium carbonate per litre (mg/L as CaCO3). A simple lab test or a field test kit gives the number. Test both the raw supply and the water after any treatment, because hardness can change with the season and the source. These are the bands commonly used to describe it.
- Soft: under 60 mg/L
- Moderately hard: 61 to 120 mg/L
- Hard: 121 to 180 mg/L
- Very hard: above 180 mg/L
Signs you have a hardness problem
You often see hard water before you test it. The signs build up slowly, so they are easy to dismiss until a heater or pump fails. In homes and housing societies, and in commercial kitchens, laundries and boiler houses, look for the following.
In industry the costs are larger. Even a thin layer of scale acts like insulation on a boiler tube or heat exchanger, so more fuel is needed to deliver the same heat. Scale also narrows cooling water lines and can block nozzles and valves. For boilers, softening the feed water is a standard part of good water treatment, not an optional extra.
- White crust on taps, showerheads and the inside of kettles.
- Spots and a cloudy film on dishes and glasses after washing.
- Pipes and showerheads that slowly lose flow as deposits build up.
- Soap and detergent that lather poorly, and clothes that feel stiff.
- Scale inside boilers, geysers and heat exchangers, which wastes fuel and can cause overheating.
How an ion-exchange softener works
A softener is a tank filled with small resin beads. The beads are loaded with sodium ions. As hard water flows through, the beads grab the calcium and magnesium and release sodium in their place. Sodium does not form scale, so the water that comes out is soft.
After a while the beads are full of calcium and magnesium and can take no more. The softener then regenerates. Strong salt water, called brine, is drawn from a separate tank and washed through the resin. The sodium pushes the hardness off the beads, the waste is flushed to drain, and the resin is ready to work again.
Time-based or meter-based regeneration
A time-based softener regenerates on a fixed schedule, for example every night, whether or not the resin is full. It is simple, but it can waste salt and water when usage is low, and run short when usage is high. It suits sites where daily water use is steady and predictable.
A meter-based softener measures the water that has passed through and regenerates only when the resin is close to its limit. It uses salt more efficiently and suits sites where demand varies. In both cases, keep the brine tank topped up with the right salt and test the outlet hardness regularly to confirm the unit is doing its job.