Water softener FAQs

Hard water is water carrying a lot of dissolved calcium and magnesium. Rain soaks through chalk and limestone on its way to the reservoirs and boreholes, and picks those minerals up. When the water's heated or left to dry, they come back out as limescale: the crust in your kettle, the white marks on taps and the build-up inside boilers and showers.

Your water supplier publishes hardness figures for every address, and you only need your postcode. Across London and the Home Counties that's usually Thames Water, Affinity Water or SES Water, and your bill tells you which. Our postcode checker gives a quick rough guide, and we test your water properly at the free survey.

On the scale we use, anything over 200 mg/l (as calcium carbonate) is hard and anything over 300 mg/l is very hard. Below 100 mg/l is soft to moderately soft. There isn't a single official UK scale, so you'll see slightly different bands on different websites. Most of London sits in the hard or very hard bands.

Divide mg/l (as calcium carbonate) by 14.3 for Clark degrees, or by 17.8 for German degrees (°dH). So 300 mg/l is about 21 °Clark or 17 °dH. Dishwashers and some softener controllers ask for one of these, so it's handy to know which your appliance wants.

No. Hard water is safe to drink, and the calcium and magnesium in it aren't a health problem. The trouble with hard water is practical: limescale on taps, showers and appliances, more soap and cleaning product needed, and a film left on glass and tiles. That's what a softener is for.

It doesn't help them. Limescale builds up wherever water is heated, so kettles, immersion heaters, combi boiler heat exchangers, washing machines and dishwashers all take a hit over time, and a coating of scale makes heating water less efficient. Our guide to limescale and your boiler goes into more detail.

A softener runs your water through a bed of resin beads that grab the calcium and magnesium and swap them for sodium. When the resin is full, the softener rinses it with salty water (brine) from its salt tank, which washes the hardness minerals down the drain and gets the resin ready to go again. That rinse is called regeneration.

No. A softener treats all the water coming into the house, so it protects every tap, shower and appliance from limescale. A filter, like an under-sink carbon filter or a reverse osmosis unit, treats the water at one drinking tap to improve the taste or remove more from it. They do different jobs, and plenty of homes have both.

They're not the same thing. A salt-based softener actually removes the hardness minerals from the water. Scale reducers and conditioners leave the minerals in and aim to change how scale forms, and how well they work varies. If you want genuinely soft water, it's a softener. Our guide on softeners versus scale reducers compares them fairly.

Whatever its manufacturer says. Most modern units take tablet or block salt, and some are designed for one only, so check the handbook or the label inside the salt lid. Don't use cooking salt or road grit. Our softener salt guide explains the differences.

A softener that's sized properly for your home and supply shouldn't make a noticeable difference to your pressure or flow. If pressure drops after a softener goes in, it's usually down to sizing, a part-closed bypass valve or a blocked pre-filter, and it's worth getting checked.

Softened water has more sodium in it than the water that went in, so the official advice is to keep one unsoftened tap for drinking and cooking. The Drinking Water Inspectorate advises keeping an unsoftened supply to the kitchen tap. That's why we fit a hard-water drinking tap in the kitchen with every softener.

Roughly 46 mg/l of sodium for every 100 mg/l of hardness it takes out. So the harder your water, the more sodium ends up in the softened water. In very hard areas, fully softened water can go over the 200 mg/l legal limit for sodium in drinking water. Our post on drinking softened water walks through the numbers.

200 milligrams per litre, measured at the tap. That limit is in Schedule 1 of the Water Supply (Water Quality) Regulations 2016 for England. It's one reason softened water isn't a good idea for your main drinking tap in hard-water areas.

No. The NHS guide on how to make up a feed says not to use artificially softened water, and the Drinking Water Inspectorate says the same. Use fresh water from your unsoftened kitchen tap, boiled as the NHS guidance describes. If you've a baby on the way, our new baby and hard water guide covers bath time too.

There's no good evidence that it treats eczema. The main UK study, the Softened Water Eczema Trial published in 2011, didn't find that softeners reduced eczema severity in children when it was assessed independently. Some families just find softened water nicer for bathing. A softener isn't a medical treatment, so talk to your GP or pharmacist about any skin condition.

Keep a dedicated hard-water tap at the kitchen sink for drinking and cooking. If you'd like water that tastes cleaner, an under-sink carbon filter reduces chlorine taste, and a reverse osmosis unit takes out most dissolved minerals, sodium included. Our sodium explainer sets out the options side by side.

Yes. Under regulation 5 of the Water Supply (Water Fittings) Regulations 1999, a water treatment unit that uses water to regenerate, which includes salt-based softeners, has to be notified to the water supplier before work starts. Reverse osmosis units are on the same list. The supplier has ten working days to respond. We'll explain how the notice works for your home when we quote.

The Water Supply (Water Fittings) Regulations 1999 cover how it's connected, including protection against water flowing back into the mains. Water Regs UK (formerly WRAS) publishes guidance on meeting them. The Drinking Water Inspectorate also advises using a qualified plumber and checking that the unit meets the fittings regulations before you buy.

As close as possible to where the mains comes in, usually under the kitchen sink, in a utility room, a garage or a cupboard. It needs a connection to the incoming main, a drain for the regeneration water and, for electric models, a plug socket nearby. We'll find the best spot at the free survey. Our installation page covers the details.

Often, yes. It depends on where your supply comes in, whether your flat has its own stopcock and incoming pipe, and whether there's room near it with a drain. In some blocks the supply is shared, and then it's a conversation with the building manager first. We'll tell you straight at the survey whether it'll work.

Usually not quite every one. It's normal to keep the kitchen drinking tap on unsoftened water, and outside taps are often left on hard water too, since there's no need to soften water for the garden. Some boiler makers also ask for the sealed heating circuit to be filled with unsoftened water, so it's worth checking your boiler's instructions.

Yes, a yearly service suits most homes. The Drinking Water Inspectorate says a regular service agreement is worth considering when you buy a water treatment unit. A service checks the softener is still softening, cleans the brine tank and injector, and catches worn seals early. See what's included on our servicing page.

The tell-tale signs are limescale coming back on taps and the kettle, salt that hasn't gone down for weeks, water sitting high in the salt tank, or an error on the display. A salt bridge, a blocked injector or a clock reset after a power cut are common causes. Our troubleshooting checklist has a few things you can safely check first.

The main running costs are salt, the water used in regeneration, electricity for electric models, and an annual service. How much salt you'll get through depends on how hard your water is and how much your household uses. We don't quote average figures, because homes vary too much, but our running costs guide explains each part.

Reverse osmosis systems need their filters changed and the system sanitised about once a year. UV lamps and their quartz sleeves should be replaced yearly too, because a lamp can still glow after it's stopped working properly. Under-sink carbon cartridges typically last 6 to 12 months, depending on use. We can usually do these on the same visit as a softener service.

It depends on your home, your water and the unit that suits you, so we don't publish a price list. We start with a free survey and water test, then give you a clear, fixed quote in writing. No pressure, and no obligation to go ahead. Ask for a free quote.

Use our online booking form to pick a weekday and a morning or afternoon slot, at least 72 hours ahead, and we'll ring to confirm. Saturdays and anything urgent, like a leak, go through the phone on 020 3633 6064, Monday to Friday, 8am to 6pm.

No. We service and repair all the major brands of softener, reverse osmosis unit and UV system, including ones that came with the house. If you can find the make and model, mention it when you book. Just moved in? Our guide to buying a house with a water softener is a good starting point.

Very likely. We cover all of London inside the M25, plus Surrey, Kent, Essex, Hertfordshire, Buckinghamshire and Berkshire. We're based in Chiswick, W4. If you're not sure whether you're in our patch, our postcode checker will tell you, or just give us a ring.

We're the home water arm of DS Water, based at The Lightbox, 111 Power Road, Chiswick, London W4 5PY. HomeWaterSoftener.co.uk is a trading name of DS Water. You can read more about us, or call 020 3633 6064.