Water Filter vs Water Softener: Which Does Your Home Need?

A water softener removes the calcium and magnesium that make water hard, which is what stops limescale forming on taps, showers, kettles and inside boilers and cylinders. A water filter improves the taste and smell of water by removing chlorine, sediment and some other substances, but most filters leave the hardness in. So the right choice depends on the problem: limescale points to a softener, taste points to a filter. In London, where most homes are on hard water, many households end up with a softener for the house and a filter on the kitchen drinking tap.

What each one actually does

There is a third option in between. A scale inhibitor or scale-reducing filter does not remove hardness but changes how it behaves, so less scale sticks to heating surfaces. It is cheaper and smaller than a softener, and it is often fitted to protect a combi boiler, but you will still see marks on taps and glass.

Which one fixes your problem?

• White crust on taps, shower heads and screens; a furred kettle: hardness. A softener fixes it; an inhibitor reduces it.
• Immersion heaters or boiler heat exchangers scaling up: hardness. A softener or inhibitor protects them. If hot water is already struggling, see our guide to hot water running out quickly.
• Water tastes or smells of chlorine: a carbon filter on the drinking tap.
• Bits or cloudiness from the tap: often sediment or air. A sediment filter helps, but if it started suddenly, check with your water company first, as it may be work on the mains.
• Dry skin, soap not lathering: hardness. A softener is what makes the difference.

Types of water filter system for a house

Jug and tap-end filters

No plumbing needed. Fine for improving taste, but cartridges need frequent changing and they do nothing for limescale around the house.

Under-sink filters and filter taps

A cartridge fitted under the kitchen sink, feeding either a separate small tap or a three-way tap that gives hot, cold and filtered water. This is the most popular way to get better drinking water, and it pairs well with a softener because the filtered tap can be fed from the unsoftened supply.

Reverse osmosis units

These force water through a fine membrane and remove much more than a carbon filter, including most of the hardness. They produce drinking water slowly, need a storage tank under the sink and send some water to drain, so they suit drinking water only, not the whole house.

Whole-house filters

Fitted on the main supply after the stopcock, usually as a sediment cartridge followed by carbon. Every tap in the house gets filtered water. They make sense if sediment is clogging appliances or you want chlorine removed from showers as well, but they do not soften water and cartridges must be changed on time, or flow and pressure drop. If your pressure is already poor, read our low water pressure guide first.

When it makes sense to fit both

If you have hard water and you want better drinking water, fitting both is the usual answer. The softener goes on the main supply to protect the boiler, cylinder, showers and appliances. The kitchen cold tap is left on unsoftened water, because softened water contains extra sodium and is not recommended for making up baby feeds, and that tap can have its own filter.

The plumbing needs planning so the drinking tap branch comes off before the softener. That is simple in a new kitchen or when the pipework is exposed, and trickier in a flat where the supply comes up through a riser with little space.

What installation involves

• Location. Softeners and whole-house filters go close to where the mains enters, often under the kitchen sink, in a utility room, or in a cellar in older London terraces.
• A drain. Softeners flush brine to waste when they regenerate, and reverse osmosis units send water to drain, so they need a waste connection nearby.
• Power. Many softeners need a socket; some non-electric models do not.
• Bypass and isolation valves so the unit can be serviced without cutting off the water.
• Backflow protection. Water treatment units must be fitted to the water fittings regulations, including a non-return valve. Some units that discharge to drain must be notified to the water company before installation.

Our plumbing labour is £95 an hour, and the call-out fee is waived when a job runs over two hours. The installer should confirm the full price, including the unit, before starting. For more on softeners specifically, see our water softener guide and our water softener installation service.

Is it worth it in London?

London's mains water is treated to drinking water standards, so a filter is about preference, not safety. For most homes, the bigger payoff comes from dealing with hardness, because limescale builds up in boilers, cylinders, immersion heaters, shower valves and appliances. If you only have a combi boiler to protect and the tap marks don't bother you, an inhibitor may be enough. If you want the whole house free of scale, a softener is the one that delivers it. Add a drinking-water filter if taste matters to you.

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