14 Litre Resin
1–6 People
15mm Install Kit Included
Metered Control
Part G Compliant
Free BWT Commissioning
The BWT WS355 is a compact, fully automatic metered water softener with a 14-litre resin capacity, designed and developed specifically for UK homes and plumbing systems. It removes the calcium and magnesium minerals responsible for limescale and scum by passing hard water through an ion exchange resin bed, delivering BWT Luxury Water throughout your home — softer on skin and hair, kinder to appliances, and gentler on surfaces. The WS355 is the standard-flow model in the BWT WS range and is supplied complete with a 15mm installation kit as standard, making it ideal for conventional gravity-fed and combi boiler systems.
Metered control means the unit regenerates only when the resin is exhausted based on actual water usage — not on a fixed timer — resulting in lower salt and water consumption compared to time-clock softeners. The AMECS (Advanced Memory Electronic Control System) retains all settings for up to 72 hours during a power failure. Supplied with a 5-year parts, 2-year on-site labour warranty and free BWT commissioning — a BWT engineer will visit your home to set up and commission the unit after installation.
Key Features
💧 Metered Regeneration (AMECS)Regenerates only when required based on actual litres used — not on a timer. The Advanced Memory Electronic Control System adapts to your household's water consumption patterns, using the minimum salt and water for each cycle. Memory retained for up to 72 hours during power failure.
🔧 Rotary Valve — Maximum ReliabilityFitted with BWT's Millennium Rotary Valve — a bespoke valve unit with fewer moving parts than multi-port designs. Fewer moving parts means fewer potential failure points and a longer service life. The valve is exclusive to BWT and serviced by BWT engineers.
🏠 Fits in a Kitchen CupboardAt 602mm high, 270mm wide and 480mm deep, the WS355 is designed to fit under a standard kitchen sink or in a utility room cupboard. Its compact footprint makes it one of the most space-efficient softeners in the BWT range.
📦 15mm Installation Kit IncludedSupplied as standard with a full 15mm hose and valve installation kit. Suitable for conventional gravity-fed vented systems and combi boilers with 15mm pipework. For systems requiring 22mm high-flow connections, see the WS455 or WS555 models.
🆓 Free BWT @Home CommissioningEvery WS355 qualifies for free at-home commissioning by a BWT-trained engineer. The engineer will configure the softener to local water hardness conditions and household requirements, and walk the customer through the unit — removing the burden from the installer.
🏆 5 Year Parts / 2 Year Labour Warranty5-year parts warranty and 2-year on-site labour warranty as standard. Register the product with BWT within 100 days of purchase to activate the extended @Home warranty offer. BWT's warranty package is among the most comprehensive in the domestic softener market.
⚡ 220V AC / 12V DC Low VoltageMains powered via a 220V AC transformer — the control unit itself operates at a safe 12V DC low voltage, meaning there is no high-voltage wiring at the control head and no risk of electric shock from the unit during normal operation or salt top-up.
🧂 Block & Tablet Salt CompatibleCompatible with both tablet salt (up to 16 tablets capacity) and block salt, giving flexibility in salt type and sourcing. Uses 1.2–2.4kg salt per regeneration cycle depending on water hardness setting.
Technical Specifications
| Specification |
WS355 Detail |
| Resin Volume |
14 litres |
| Dimensions (H × W × D) |
602mm × 270mm × 480mm |
| Household Size |
1–6 people |
| Min Flow Rate |
10 l/min |
| Service Flow Rate |
25 l/min |
| Peak Flow Rate |
30 l/min |
| Max Pressure |
5 bar |
| Min Pressure |
1.7 bar |
| Max Water Temperature |
49°C |
| Inlet / Outlet Connection |
¾" BSP |
| Drain Connection |
½" tube |
| Installation Kit Included |
15mm hoses and valves (standard gravity/combi systems) |
| Salt per Regeneration |
1.2–2.4 kg (min/max) |
| Salt Type |
Tablet salt (up to 16 tablets) |
| Max Softened Water Capacity |
2500 litres |
| Electrical Supply |
220V AC / 12V DC (transformer included) |
| Regeneration Type |
Metered — demand-initiated (AMECS) |
| Regeneration Direction |
Upward flow |
| Memory Backup |
Up to 72 hours during power failure |
| Colour |
Blue & Grey |
| Warranty |
5 years parts / 2 years on-site labour |
| Building Regulations |
Part G compliant |
| Brand |
BWT |
Frequently Asked Questions
What is the difference between the WS355 and WS455?
The WS355 is the standard-flow model with a 14L resin capacity and 15mm installation kit — peak flow rate of 30 l/min. The WS455 is the hi-flow model with a 10L resin capacity and 22mm installation kit — peak flow rate of 50 l/min, making it better suited to power shower systems, unvented (Megaflow) systems, and modern high-pressure plumbing. If your system uses 22mm pipework or you have a high-flow demand, the WS455 is recommended over the WS355.
Does the softener need a separate drinking water supply?
Yes — Building Regulations (Part G) require that at least one tap in the property continues to supply unsoftened (hard) mains water for drinking. This is typically the kitchen cold tap. The water softener should be plumbed in on the inlet side, with a branch taken off before the softener to the kitchen cold drinking tap. The WS355 is Part G compliant when installed correctly with an unsoftened drinking tap as required.
How often does it regenerate and how long does it take?
The WS355 regenerates based on actual water consumption (metered) — typically every few days for an average household, but the exact interval depends on local water hardness and daily usage. Regeneration takes approximately 110 minutes and is typically set to occur at night during low-demand periods. The unit is programmed to the local water hardness level during commissioning.
Is free commissioning really free?
Yes — BWT offers a free @Home commissioning service with the WS355. After purchase and installation, you book a visit from a BWT-trained commissioning engineer who will set up the unit to your local water hardness, demonstrate operation, and answer any questions. This service is free and is available directly from BWT. The product must be registered with BWT within 100 days of purchase to activate the full @Home warranty and commissioning offer.
⚠️ Note: The WS355 is supplied with a 15mm installation kit. For 22mm high-flow systems (unvented/Megaflow), consider the WS455 or WS555. An unsoftened drinking water tap is required by Building Regulations Part G — this must be installed as part of the water softener installation. Register within 100 days of purchase for the full BWT @Home warranty.
