Water Softener Salt: Block vs Tablet vs Granular

Which type of salt does your water softener actually take?

Check the manual, because the machine dictates the format. Block salt suits twin-cylinder non-electric units from Harvey and Kinetico. Tablet salt suits most electric metered cabinets — BWT, Monarch, Tapworks and Water2Buy. Granular goes in units that specify it. Some models, such as BWT's WS355, accept either block or tablet.

Settle this before you buy the machine rather than after, because it sets the refill routine for as long as you own it. Block salt is bought as solid lift-in blocks; tablet and granular come in sacks you pour. A tablet cabinet has a wide salt store you tip a bag into; a block machine has two shaped recesses.

Getting it wrong is not merely inconvenient. Salt blocking the brine valve is one of the most commonly reported softener faults, alongside the unit regenerating more often than it should — and both start with the wrong or poor-quality salt in the brine tank. If you are still choosing, which water softener to buy sets out which model takes which format.

• Block salt — Harvey and Kinetico twin-cylinder non-electric machines, plus some compact units
• Tablet salt — BWT, Monarch, Tapworks and Water2Buy electric metered cabinets
• Granular salt — budget and older electric units that specify granular in the manual
• Either block or tablet — dual-format models such as the BWT WS355

Block salt vs tablet salt: what is the real difference?

Handling and price, mostly. Block salt is lighter to lift, cleaner to load and easier to store, but costs more per kilo and only works in machines designed for it. Tablet salt is the cheapest mainstream option and fits the majority of electric metered softeners, at the cost of hauling 25kg sacks.

Neither format softens better — the ion exchange inside the resin cylinder is identical. What differs is living with it. Block owners describe refilling as a two-minute job; tablet owners describe it as cheaper but heavier. If you have a bad back or an awkward under-sink cupboard, that is worth more than the price gap.

Format also tracks the brand split: a block-salt machine means the dealer-installed twin-cylinder route, which we cover in Harvey vs Kinetico vs BWT.

When is granular salt the right choice?

Only when your softener's manual asks for it. Granular is the cheapest format and works well in the budget electric units that specify it — the Water2Buy W2B200, for example, runs on cheap granular or tablet salt. In a machine designed for tablets or blocks, granular is a false economy.

The difference is grain size. Granular dissolves readily, which is what a compatible unit wants, but a finer grain in the wrong brine tank is more prone to compacting into a crust or leaving sludge — the failure mode that ends in a blocked brine valve.

If your manual lists granular as acceptable, purity rather than format is the thing to be fussy about.

Does salt purity matter, and what is grade A?

It matters more than the format. Buy high-quality grade A salt at 99%+ purity, which is the standard specification for softener salt in the UK. The impurities in lower-grade salt are what settle out as sludge in the brine tank, and sludge is what eventually fouls the brine valve.

Grade A, 99%-plus purity is the benchmark on the bag, and virtually all salt sold specifically as water softener salt in the UK meets it. Do not substitute salt sold for other purposes because it looked cheaper — dishwasher, cooking and de-icing salt are different products and none is what your manual asks for.

The payoff is a brine tank you rarely think about. Most reported softener problems — regenerating more than normal, salt blocking the brine valve, condensation inside the cabinet — are maintenance faults rather than mechanical failures, and clean high-purity salt removes a large share of them.

How much salt will a UK household get through?

In a typical hard-water home, expect a refill every four to six weeks. Real figures owners and manufacturers report range from around 1.2–2.4kg per regeneration on a BWT WS355, to a 25kg bag every five to six weeks on a high-capacity Water2Buy W2B800, to roughly a block a month on a compact block-salt unit.

Usage is driven by hardness, how much water you use, and how efficiently the softener regenerates. Every softener we rank uses metered demand regeneration, which only runs when the resin has actually been used and is markedly cheaper than old timer-based machines. Some go further: the Monarch Midi HE Opti-Brining regenerates only the resin used, which Monarch says cuts water use by up to 24% and salt by around 12% a year.

Undersizing a softener means constant regeneration and more salt, while a big salt store simply means fewer trips to the garage — the Tapworks AD11 holds 37kg, so refills are infrequent even though usage is ordinary. That trade-off is covered in our ranking of which water softener to buy.

What does softener salt cost per year?

Budget roughly £5–£10 a month in a typical hard-water household, so about £60–£120 a year. Tablet and granular salt are cheapest per kilo, block salt dearest. Add a small amount of water used during regeneration, and, on electric units, modest electricity — a Water2Buy W2B200 is quoted at around £20 of electricity a year.

Set against the purchase price, salt is the small number. An Amazon-supplied electric metered softener runs roughly £300–£800 depending on capacity, plus £150–£350 if a plumber fits it, while a dealer-installed twin-cylinder system typically costs £1,500–£2,500 installed — our running and installation costs page breaks that down.

Efficiency differences are real but modest in cash. Harvey quotes 50% salt efficiency against Kinetico 35%, and around 17 litres of water per regeneration against Kinetico 20.5 — meaningful between two premium machines, not the number that decides whether to buy at all. The saving owners raise most is not the salt: it is using less soap, shampoo and washing powder.

How do you top up salt without blocking the brine valve?

Use grade A 99%+ salt in the format your manual specifies, top up before the tank runs empty, and check for crusting when you refill. Salt blocking the brine valve is a recurring owner complaint, and it almost always starts with poor-quality salt or a tank left to compact.

None of this is difficult, but it is the difference between a softener you forget about and one that needs a callout.

If the machine starts regenerating noticeably more often than it used to, treat the salt as the first suspect. Regenerating more than normal and salt blocking the brine valve are the two faults that dominate aggregated owner reviews, and they are related — a fouled valve stops the unit drawing brine properly, so it tries again.

Salt will not clean up what has already scaled: if your kettle is furred solid, see how to descale a kettle. And if you are fitting alongside a combi, the filling rules in fitting one to a combi boiler matter more than the salt choice.

1. Buy grade A salt at 99%+ purity, in the format your manual specifies
2. Never substitute dishwasher, cooking or de-icing salt
3. Top up before the tank empties rather than after
4. Look for a crust or bridge across the salt when you refill, and break it up
5. Do not mix formats in the same tank unless the manufacturer says the machine takes both
6. Keep the lid on between refills to keep dust and damp out
7. If regeneration frequency changes, check the brine tank and valve before calling anyone