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How to install a water softener

Updated: 17.10.2026

Knowing how to install a water softener starts before anyone cuts the rising main. A salt unit needs a cold feed, a bypass, an untreated kitchen drinking tap, a brine drain with an air gap, and a visible overflow. If you cannot see where each connection will go, hand the job to a qualified plumber. Peter F. used amazon.co.uk extracts from 15 October 2026 and public UK sources. There was no laboratory test. Identify the unit on the [water softening systems comparison](/hub/hot-water/water-softening-systems), then give its current manual to the person doing the work. A qualifying purchase through our links can earn us a commission at no extra cost to you.

Knowing how to install a water softener starts before anyone cuts the rising main. A salt unit needs a cold feed, a bypass, an untreated kitchen drinking tap, a brine drain with an air gap, and a visible overflow.

Our top picks

AquaHouse AquaHouse 9 litre

Best overall

AquaHouse AquaHouse 9 litre
7.1/10about £399.99
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BWT BWT WS355

Rank 2

BWT BWT WS355
8.9/10about £599
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Eddy Eddy ED6002P-UK

Alternative

Eddy Eddy ED6002P-UK
8.1/10about £139
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On this page
  1. 1.Make sure the site has what the unit needs
  2. 2.Keep the drinking tap upstream of the bypass
  3. 3.Provide a drain air gap and a visible overflow
  4. 4.Understand what the box includes

Make sure the site has what the unit needs

Choose a position close to the incoming cold main, a suitable drain and, for powered models, a safe BS 1363 socket. The cabinet must clear real obstructions and leave room for the lid, salt filling, the bypass and later servicing. A 583 mm appliance does not sit comfortably under a 585 mm shelf once pipe bends and lid clearance are included. Measure the doorway and the plinth as well as the final space. Map the drain and the overflow before you order. A salt softener discharges brine during regeneration and also needs a separate route that makes an overflow fault visible. A washing-machine spigot that is already in use is not proof that both connections can be made. Size and approval checks come first, on the water softener buying guide.

Keep the drinking tap upstream of the bypass

Southern Water’s fittings guidance describes a drinking tap over the kitchen sink connected before the softener, with a servicing valve, a bypass and inlet protection. That preserves an untreated cold supply for drinking and cooking. The bypass lets you isolate the softener while the rest of the house still has water. The hard branch has to stay upstream of the softener, so it does not become softened when the bypass is in normal service. Ask the plumber to label the valves and show you the operating positions. Three similar handles at the back of a cupboard are easy to misread during a leak. AquaHouse advertises an integrated bypass, and that does not design the surrounding pipework. Pipe material, bore, check valves and access still depend on the property. If you cannot trace which branch serves the kitchen tap, stop there.
AquaHouse AquaHouse 9 litre

Testsieger

AquaHouse AquaHouse 9 litre
7.1/10about £399.99
View offer

Provide a drain air gap and a visible overflow

WRAS installation guidance for ion-exchange softeners calls for an air gap of at least 20 mm on the brine drain, or twice the drain-tube diameter when that is greater. The gap stops contaminated water being drawn back into the drinking supply. A hose pushed tightly into a waste fitting is not an air gap, even when it looks secure. The overflow is a separate safety route: at least 15 mm, with a free fall through an outside wall so a fault is visible. It is not the routine regeneration discharge. Do not merge the two jobs. BWT reviews mention two waste connections, including a rigid overflow and a hose that missed a washing-machine spigot. Check the current WS355 manual against a photograph of the site. Do not tee into a soil pipe or hide the overflow. If the air gap, the fall or a visible outlet is missing, a qualified plumber should own the design.

Understand what the box includes

The AquaHouse 9 litre listing mentions an integrated bypass and a two-metre drain hose. Those parts do not include a compliant air gap, an overflow, or a guarantee that two metres reaches a suitable waste. Regeneration salt is extra. Confirm whether inlet hoses, adaptors, isolation valves and commissioning materials are in the box for your exact model. BWT reviews show a compact cabinet can still need a cupboard cut and paid remedial work. Do not cut pipe for the iSpring until a current drawing settles the conflicting dimensions. Those limits are on the best water softener UK page. Eddy and Water-King wrap a coil, with no resin, salt or brine drain. A no-plumber claim on Eddy does not describe a salt unit. That choice is the salt water softener vs electronic descaler page. If you are not competent to alter the supply, hand the model, manual, hardness figure, measurements and drain route to a qualified plumber, and keep the valve positions in writing.

Common questions

Can I fit a salt water softener myself?
Only if you are competent to alter drinking-water pipework and can meet the appliance and water-fittings requirements. The job is more than joining two hoses. It includes inlet protection, bypass operation, an untreated kitchen tap, a brine-drain air gap and a visible overflow. Otherwise, use a qualified plumber.
Where should the unsoftened drinking tap connect?
Connect it upstream of the softener and its bypass, normally at the kitchen sink. That keeps a suitable supply for drinking, cooking and infant-formula preparation. Ask the installer to identify and label the branch so later servicing does not change which water reaches the tap.
Why does the brine drain need an air gap?
The air gap is a physical break between the softener discharge and the waste system, so contaminated water is less likely to be drawn backwards. Guidance gives at least 20 mm, or twice the drain-tube diameter if that is greater. A hose pushed into a waste connector does not provide that separation.
Why do some BWT reviews mention two pipes?
A salt unit has a routine regeneration drain and a separate safety overflow. They do different jobs and may need different terminations. Review comments are a prompt to check the current WS355 manual and the proposed site. They are not permission to combine both outlets into one improvised fitting.
Does AquaHouse include everything needed?
The researched listing mentions an integrated bypass and a two-metre drain hose. It does not include salt, a complete air-gap assembly, or every adaptor your pipework may need. Installation cost depends on the property. Obtain an itemised quote against the exact model before you treat the shelf price as the total.

Related pages

Water softener for limescale and hot water

Water softening systems

Best water softener UK: top pick and who should skip

Water softener buying guide for a UK hard-water home

Salt water softener vs electronic descaler, explained

Sources

Public UK sources from the digest of 16 October 2026, and amazon.co.uk extracts dated 15 October 2026.

  1. Drinking Water Inspectorate: domestic water filters and softeners (retrieved 16 October 2026)
  2. Drinking Water Inspectorate: water hardness (retrieved 16 October 2026)
  3. Drinking Water Inspectorate: hardness map (retrieved 16 October 2026)
  4. Drinking Water Inspectorate: drinking water standards (retrieved 16 October 2026)
  5. NHS: making up baby formula (retrieved 16 October 2026)
  6. DWQR Scotland: water conditioning (retrieved 16 October 2026)
  7. WRAS approvals directory, section 2450 (retrieved 16 October 2026)
  8. Which?: how to buy the best water softener (retrieved 16 October 2026)