How to live without limescale

Should every home have a water softener, or are they just costly gadgets? Jeff Howell takes a hard look at the facts

WATER softeners seem to be the latest must-have gadget for the modern home. Just when you thought you had every major item - washing machine, fridge/freezer, dishwasher - along comes a sales leaflet through the door, and you wonder whether you're missing out.

More and more people are getting water softeners - trade association British Water estimates that more than 300,000 have been installed in the last 15 years - but there is still some resistance to paying up to pounds 1,000 for what some see as an unnecessary luxury. The marketing of some retailers - leafleting homes and cold-calling, like double-glazing salesmen - have done nothing to quell doubts about the real need for a salt-guzzling gadget under the kitchen sink.

But water softeners do have measurable advantages. They prevent limescale forming, and stop the kettle furring up - and the coffee machine and the shower head - so there's a saving in descaling time and chemicals. And if you think kettle scale is a nuisance, imagine what the inside of your boiler and hot water cylinder look like. It is claimed that water softeners, by preventing limescale, make heating appliances more efficient and lower fuel costs. There is also a potential saving of up to 50 per cent in soap and detergent costs, and less time and effort spent on cleaning. Soft water is kinder to clothes. There are even claims that softened water helps skin complaints, including eczema.

Put like this, softeners start to sound like economic sense, and worth a look. But first, some basics: what is hard water and soft water, and what is the best way to convert one into the other?

All our water arrives by falling from the sky. Rainwater is naturally "soft" - it lathers easily with a small amount of soap, and things dissolve easily in it. As rainwater percolates down through the land and flows as streams and rivers, it dissolves minerals from the earth. In 60 per cent of Great Britain - roughly south-east of a line from the Humber down to Dorset - these minerals include chalk and limestone, and it is these that make water "hard".

The dissolved lime - chiefly calcium carbonate and magnesium carbonate - combines with soap to form a hard scum and, when heated in the kettle, gets left behind on the element as scale. Even when hard water evaporates at low temperatures, it will leave spots of white limescale residue - on the just-washed car, on plates and glasses, and as little stalactites growing out of the bath taps.

Water hardness is measured by the total concentration of calcium, in milligrams per litre (mg/L). "Soft" water has less than 50 mg/L, "hard" water more than 250 mg/L. In between is "moderately hard", where it may or may not be worthwhile installing a water softener. Dr Simon Parsons, of Cranfield University, a water sciences expert, thinks 150 mg/L is a good cut-off point. So the first thing is to ask your water company for a free analysis of your supply.

If your water is above 150 mg/L, you are then faced with a range of models. Domestic water softeners all work on the ion exchange principle. They consist simply of a vessel containing resin-coated plastic beads with sodium ions on their surface, and when water passes over them they pick up the sodium and leave the calcium ions behind. After a time the resin beads must be regenerated by flushing through with common salt solution (sodium chloride), so there is another vessel containing salt. A small home softener will use around 2 kilograms of salt per flush, or a 25 kilo bag a month. Salt costs about pounds 9 a bag from DIY superstores, but local suppliers may deliver it for half this price.

The differences between the various softeners on the market mainly concern the different ways in which the salt flush works. The cheapest domestic softeners, at around pounds 400, rely on a time switch to flush through on a regular basis; the more sophisticated, costing up to pounds 1,000, use microprocessors to monitor water flow and the state of the resin beads, and should be more economical with salt. Water cannot be used while the salt flush is taking place, so this is normally timed to occur at night, but a further sophistication is the twin-vessel softener, which has one vessel in use while the other is being flushed through.

Plumbing in should be straightforward, but softened water is not generally suitable for drinking, from either a taste or a health perspective, so separate pipework should be installed to deliver non-softened drinking water to the kitchen sink and bathroom washbasin.

British Water provides a free consumer pack with video outlining the advantages of water softeners and giving a list of suppliers. In addition, ex-army Major Martin Briggs makes his own water softeners - he claims to use the same materials and parts as the big manufacturers, and his prices start at pounds 300.

There are other, cheaper, devices on the market called scale inhibitors or "physical conditioners". These do not claim to produce softened water, but use a variety of electrical or magnetic methods to change the physical structure of the calcium ions so that they do not form scale. Scale inhibitors are widely used in industry, but there is as yet no published scientific work confirming their efficacy in domestic situations.

q 'A consumers' guide to water softeners' is available from British Water, tel: 0171-957 4554. Major Martin Briggs, trading as Briggs Enterprises, tel: 01296 670351. Information on electro-sonic scale inhibitors from BW Technologies, tel: 0990 820000.