Water Softener Installation: Bypass Valves, Drinking Water & Waste Connections

Summary

Hard water affects roughly 60% of UK homes, particularly in southern England, East Anglia, and the Midlands. Water hardness (measured in ppm or mg/l of calcium carbonate, or degrees of hardness in Clarke degrees) causes limescale deposits on heating elements, in boilers, and in pipes, reducing efficiency and lifespan. Water softeners replace calcium and magnesium ions (which cause hardness) with sodium ions through an ion exchange resin, producing soft water that dramatically reduces scale formation.

Water softener installation is a plumbing job with specific regulatory requirements that are frequently overlooked. The key compliance point is that softened water must not be used as a sole drinking water supply — it has elevated sodium content, which is a dietary concern, particularly for those on sodium-restricted diets and for infants. A separate unsoftened mains water supply to the kitchen cold tap is therefore mandatory.

The Water Supply (Water Fittings) Regulations 1999 and WRAS guidance govern water softener installation. The unit must be WRAS-approved (or the installation must be notified to and approved by the water company), the waste connection must be made correctly to prevent back-siphonage, and a bypass arrangement must be provided to allow the property to have a water supply when the softener is being serviced or if it malfunctions.

Key Facts

• Water hardness measurement — Parts per million (ppm) or mg/l of calcium carbonate (CaCO3); also expressed in Clark degrees (1° Clark = 14.3 ppm)
• Soft water — Less than 100 ppm CaCO3
• Moderately hard — 100-150 ppm
• Hard water — 150-300 ppm
• Very hard — Above 300 ppm (common in London, Kent, East Anglia)
• Drinking water — softened water — Should NOT be the sole drinking water supply; sodium content elevated after softening
• Unsoftened kitchen tap — Mandatory; fed directly from the incoming mains before the softener
• Bypass valve — Required; allows water to bypass the softener for maintenance
• WRAS approval — Unit must appear on the WRAS approved products list, or installation notified to the water company
• Installation position — After the main stop tap; before the distribution to other outlets (except drinking water tap)
• Salt — Block or granular salt required for regeneration; automatic regeneration on a timer or by water usage
• Waste connection — Brine waste from regeneration must connect to a trapped drain; minimum 25mm air gap or trapped sump
• BS EN 14743 — European standard for domestic water softeners
• Regeneration frequency — Depends on hardness level and usage; typical domestic softener regenerates every 2-4 days
• Softener sizing — Must be sized for daily water usage and hardness level; undersizing leads to hard water breakthrough
• Service intervals — Annual inspection; salt refill every 4-8 weeks depending on usage and softener size

Quick Reference Table

Detailed Guidance

Installation Position

The water softener should be installed:

1. After the incoming mains stop tap and any meters
2. Before the distribution pipework to the rest of the property
3. A branch for the unsoftened kitchen cold tap must be taken before the softener inlet
4. Near a drain for the waste brine discharge

Typical installation in a kitchen under the sink: the incoming cold water supply splits — one branch goes directly to the kitchen cold tap (unsoftened drinking water), the other passes through the water softener before distributing to the rest of the house.

In a utility room or garage installation, the softener is typically installed on the rising main after the cold mains stop tap, with the unsoftened kitchen cold tap branching off earlier.

Bypass Valve Configuration

A bypass is mandatory under the Water Fittings Regulations to allow the softener to be isolated and the property to continue receiving (hard) water during maintenance or faults.

Standard 3-valve bypass:

• Isolation valve on softener inlet
• Isolation valve on softener outlet
• A bypass valve connecting inlet and outlet pipework, bypassing the softener

When serviced: close both softener valves, open the bypass valve — water flows past the softener directly.

Proprietary 3-way bypass block: Many softener manufacturers supply a single 3-way bypass valve block that combines all three functions. These are tidier and reduce the risk of incorrect operation. Prefer these where available.

Drinking Water Requirement

Softened water has elevated sodium content because calcium and magnesium are replaced by sodium during ion exchange. The sodium increase depends on hardness:

The UK DWI (Drinking Water Inspectorate) recommends a maximum sodium level of 200 mg/l in drinking water. Very soft regions' softened water may stay within this limit, but in hard water areas it typically exceeds it. Furthermore, for infants under 12 months, the NHS recommends using unsoftened water for feeding formula.

The solution — a dedicated unsoftened cold tap at the kitchen sink — is both good practice and a regulatory requirement for new installations. In practice, this means retaining the existing kitchen cold tap on the direct mains supply, even if the rest of the house is softened.

Waste (Brine) Discharge

During regeneration, the softener discharges a concentrated brine (salt water) solution from the resin bed. This waste must be:

• Discharged to a trapped drain
• Via an appropriate air gap to prevent back-siphonage (contamination of the water supply)
• Not discharged into a surface water drain (salt water to surface water drains is environmentally harmful and may be prohibited by the local sewerage operator)

Acceptable discharge points:

• Under-sink waste trap (into the kitchen waste)
• Utility room floor drain (provided it has a proper trap)
• Outdoor waste pipe to foul sewer

Not acceptable:

• Direct connection to drain without an air gap or trap
• Surface water drain or soakaway
• Combined drain where the outfall goes to a soakaway (check with the installer)

The discharge connection should use a stand pipe (minimum 25mm diameter) with a free air gap above the maximum drain level — similar to an indirect connection for a washing machine waste.

Sizing a Domestic Water Softener

Softeners are sized by:

• Water hardness (ppm or Clark degrees)
• Daily water consumption (litres per day per person; typically 150-250 L/person/day)

Most manufacturers provide a sizing guide. The key output is the regeneration frequency — an appropriately sized softener should regenerate approximately every 3-7 days for a typical household.

Undersized softener: Runs out of softening capacity between regenerations; hard water breaks through Oversized softener: Regenerates infrequently; water can stagnate in the resin bed; Legionella concern if very infrequent use

Salt Management

Salt is consumed each time the resin regenerates. Block salt and granular/tablet salt are both available; the softener manual specifies the appropriate type:

• Block salt — Pre-formed blocks; clean and easy to handle
• Tablet/granular salt — Requires more frequent checking; can bridge over the salt chamber
• Salt bridges — Hardened salt crust forming over an air gap above liquid; prevents regeneration; check periodically and break down with a broom handle

Always use water softener salt, not road salt or food salt — impurities in other salt types can damage the resin.

Frequently Asked Questions

Does installing a water softener need to be notified to anyone?

The Water Supply (Water Fittings) Regulations 1999 require that certain works (including some plumbing installations that may affect the mains supply) are notified to the water company. For domestic water softener installations using WRAS-approved equipment, most water companies accept installation without prior notification, provided the installation complies with the Regulations. Always check with the local water company if you're uncertain, and keep a record of the WRAS product approval number.

Can softened water damage a combi boiler?

Softened water can actually benefit boilers in hard water areas by preventing limescale buildup on the heat exchanger. However, softened water must not be used to fill sealed heating systems directly — the elevated sodium content can accelerate corrosion in certain system materials. Heating systems should be filled with inhibitor-treated mains water (hard or soft) and the system fluid monitored. Some boiler manufacturers specify inhibitor and water treatment requirements in their warranty conditions.

My customer wants the whole house including the hot water cylinder on softened water — is this OK?

Yes, the hot water cylinder can be on the softened water supply. In fact, this is one of the main benefits — a cylinder that doesn't fur up with limescale maintains efficiency and extends its life. The only mandatory exception is the kitchen cold tap, which must remain on unsoftened mains water for drinking. Other drinking water taps (if provided elsewhere) should also be unsoftened.

How often does the salt need refilling?

This depends on water hardness, household size, and softener capacity. As a rough guide:

• 2-person household in hard water area: refill every 4-6 weeks
• 4-person household in hard water area: refill every 2-4 weeks
• Very hard water area: more frequently

Most modern softeners have a salt low indicator. Block salt softeners typically require 2 blocks per refill; granular salt softeners require the brine tank to be kept at least half full.

Regulations & Standards

• Water Supply (Water Fittings) Regulations 1999 — Governs all plumbing fittings and installations connected to the mains; softeners must comply

• BS EN 14743 — Water conditioning equipment inside buildings; household and similar use; softeners; requirements for performance, safety and testing

• WRAS Approved Products Directory — Lists water softeners approved under Water Fittings Regulations; check before installation

• DWI (Drinking Water Inspectorate) Guidance — Sodium limits and drinking water quality

• WRAS Water Regulations Advisory Scheme — Water Regulations compliance and approved products

• Water Quality Association (WQA) — Water softener technical guidance

• Drinking Water Inspectorate UK — UK drinking water standards including sodium limits

• water regulations — Water Supply Regulations 1999 overview and WRAS approval

• cold water storage — Cold water storage and treatment

• hot water systems — Boiler and cylinder systems