Do You Need a Water Softener in an Apartment or a Private House

A water softener does one job: it removes calcium and magnesium salts. It does not remove iron from water, eliminate odor or improve taste. Here we look at where it pays off, where it is unnecessary and how it is sized by the numbers.

What Happens Inside

The vessel contains a bed of ion exchange resin. Each bead carries mobile sodium ions. Water passes through the bed, calcium and magnesium are bound to the resin, and sodium goes into the water. The exchange proceeds by equivalents, not by mass.

The resin becomes saturated with calcium and stops working. The valve then starts regeneration: the bed is flushed with a brine solution, sodium displaces calcium back off the resin, and the rinse water goes to the drain. The cycle repeats. The salt consumption and the volume of water between regenerations are calculated in advance.

Control is either time-based or volume-based. A volume-based valve counts the liters passed and regenerates according to actual throughput. A timer valve regenerates on a schedule. With uneven water demand, a timer gives either hardness breakthrough or excess salt consumption.

Where Hardness Turns into Money

Calcium carbonate loses solubility when heated. That is why scale deposits where it is hot: the heating element, the boiler heat exchanger, the walls of the water heater, the nozzles of the dishwasher.

The Battelle institute, commissioned by the Water Quality Research Foundation, carried out laboratory tests of appliances on hard and softened water. According to the results of these tests, gas storage water heaters on hard water lost up to 48 percent of efficiency over their service life, tankless water heaters stopped working because of fouling after 1.6 years of equivalent water use at a hardness of 26 grains per gallon, and showerheads lost up to 75 percent of flow in less than 18 months. A hardness of 26 grains per gallon corresponds to approximately 8.9 meq/L. The conditions were accelerated and laboratory-based, so the figures cannot be transferred directly to a specific project. They do show the direction of the dependence accurately.

Apartment: Calculate Based on Water Heating

An apartment does not always need a water softener. Look at what heats your water.

• There is an individual gas boiler or an electric water heater. A water softener pays off. The boiler heat exchanger has narrow channels and a high heat flux density, and scale deposits there first.
• Hot water is centralized, there is no boiler of your own and no dishwasher. A whole-apartment water softener is excessive. Mechanical filtration and point-of-use drinking water treatment under the sink are enough.
• There is a dishwasher and a washing machine, but no heating of your own. A compromise is a compact water softener on the cold water supply line to the appliances.

Space for equipment in an apartment is limited. A compact cabinet-type water softener requires a drain connection for discharging the regeneration water and an electrical outlet. These two points are checked before purchase, not after.

Private House: Different Sizing

In a house the circuit is longer, there are more appliances, and the cost of a failure is higher. Here the water softener is installed on the main inlet after mechanical filtration. Three numbers determine the choice.

• The hardness of the raw water in meq/L from the analysis report.
• The peak flow rate in m³/h. It is taken from the points operating simultaneously, not from the daily average. The flow velocity through the resin bed is limited, and when it is exceeded, hardness breaks through.
• Daily water consumption. It determines how often regeneration will occur.

Next, the volume of water between regenerations is obtained by dividing the working exchange capacity of the media charge by the hardness. The working capacity is taken from the resin data sheet at the selected salt dose, not from general tables. The same resin gives a different capacity and a different salt consumption per cubic meter at a different salt dose.

Sodium and the Limits of Applicability

Ion exchange does not remove salts from water. It exchanges them. By stoichiometry, one meq of calcium is replaced by one meq of sodium, which is 23 mg of sodium per liter. With a raw water hardness of 7 meq/L, the softened water gains about 160 mg/L of sodium. WHO does not set a health-based guideline value for sodium, but it notes that above 200 mg/L the taste of the water becomes unacceptable.

Hence the practice. The kitchen faucet is left on an unsoftened line, or a separate drinking water stage is installed on it. University water treatment guides also note that softened water should not be used to water houseplants or lawns because of the sodium.

What a water softener does not do:

• it does not remove turbidity and suspended solids; for that, mechanical filtration is needed ahead of it
• it does not cope with high iron; reference materials give a guideline of up to 10 mg/L for standard resin, and above that a separate iron removal station is needed
• it does not reduce total dissolved solids or nitrates
• it does not disinfect the water

What this means for a project in Tashkent

• The water in Tashkent is hard. In our practice, in approximately 85 percent of the city and in all regions of the republic, the water is hard and of low quality. Individual districts with an acceptable composition do occur, but this cannot be relied upon in design.
• If an apartment has an individual boiler, softening pays off fastest on that boiler. Cleaning the heat exchanger and replacing it cost more than several years of salt.
• Always install mechanical filtration ahead of the water softener. Suspended solids and scale from the old city mains shorten the service life of the resin.
• Run the kitchen faucet on a separate line. Drinking water is produced by point-of-use treatment, not by a water softener.