Advanced options
Only worth reading in a hard-water area (roughly the south and east of England: your water company's website states your hardness). The case: scale coats heating elements (a millimetre of scale costs several % of boiler efficiency), kills kettles, showers and appliances early, and doubles cleaning-product use. The small print: softened water isn't for drinking taps in the classic sodium-exchange setup (a hard drinking tap is standard practice), and combi boiler manufacturers vary on warranty terms: check yours.
What The Water Softener Calculator Works Out
- Running cost per year: people x 3.5 bags of salt a year x the bag price. A four-person household gets through a 25kg bag roughly every three to four weeks at GBP 7 to GBP 12 a bag, so GBP 100 to GBP 150 a year.
- What hard water costs you: a conservative GBP 100 a year plus GBP 25 per person for lost boiler efficiency (a millimetre of scale costs several per cent), early deaths of kettles, shower heads and appliances, and doubled cleaning-product use.
- Verdict: the scale estimate minus the salt bill, and how many years that saving takes to repay the GBP 800 to GBP 1,800 installed unit. Softeners roughly wash their face over five to ten years; the comfort and the end of limescale as a category of housework are the real sell.
- Water hardness (advanced): scales the damage estimate to your supplier's figure. Over 300 mg/l (much of Kent, Essex and the Chilterns) adds 25%; moderately hard water cuts it to 60%; in soft-water Cumbria or Wales the same unit is an expensive curiosity.
- Salt use and servicing (advanced): metered and twin-cylinder units use less salt than the 3.5 bags per person default, block-salt units a little more per kilo of hardness removed. Optional annual servicing runs GBP 60 to GBP 100.
- Regeneration water (advanced): each regeneration flushes 50 to 150 litres to the drain; two or three a week is typical. On a meter that water plus sewerage costs about GBP 3.50 per cubic metre, which most brochures forget.
- All-in running cost and cost per year over its life (advanced): salt, servicing and regeneration water together, then the installed price spread over a 15-year lifespan on top, which is the true weekly cost of soft water.
- Payback including servicing (advanced): the installed price divided by the scale cost avoided after all running costs. Use the custom scale-cost field if you have a real figure, such as a replaced heat exchanger or a dishwasher that died at four years.
- Scale inhibitor instead (advanced): an inline polyphosphate cartridge at GBP 80 to GBP 150 fitted plus GBP 20 a year protects the boiler alone, roughly a third of the scale cost, and does nothing for showers, kettles or cleaning. It is cheap boiler insurance, not a softener.
- Cumulative table (advanced): softener spend against scale cost avoided at years 1 to 15, showing where the lines cross and whether they cross before the unit needs replacing.