Water Softener Salt: Which Type Should You Use?

Block salt comes in rectangular compressed blocks, typically sold in pairs. It is the type used by Harvey, Kinetico, and most non-electric twin-cylinder systems. The blocks sit in the brine cabinet and dissolve slowly as the softener draws brine during regeneration cycles.

Block salt is convenient — it is clean to handle, easy to stack, and produces less mess than loose alternatives. Harvey's proprietary curve salt blocks are specifically shaped for their units, but many compatible block salts from other manufacturers work equally well at considerably lower cost. Standard block pairs typically cost £5 to £10 from independent suppliers, compared to £15 to £25 for branded Harvey packs.

Tablet salt is the most widely used type for electric and metered water softeners. The tablets are similar in size and shape to dishwasher salt tablets, sold in 25kg bags. This is the type loaded into the brine tank on most single-tank electric softeners from brands like Monarch, BWT, and Water2Buy.

Tablet salt is available almost everywhere — B&Q, Screwfix, Amazon, and most plumbers' merchants stock it. A 25kg bag costs around £8 to £14. The low cost and wide availability are the main practical advantage of tablet salt over blocks.

Granular salt is less commonly used in domestic softeners than tablets or blocks, but some older systems and commercial units specify it. It dissolves more quickly than tablets, which can be an advantage in high-demand applications but can also lead to bridging issues (see our guide to salt bridges) in systems not designed for it.

Unless your softener's manual or manufacturer specifically recommends granular salt, stick with tablets or blocks as appropriate for your unit. Using the wrong salt type will not damage the resin but can cause operational problems.

Salt usage depends on your water hardness, household size, and whether your softener is metered (regenerates based on water used) or timer-based (regenerates on a fixed schedule). A typical four-person household in a moderately hard water area uses:

• Block salt: roughly one block per person per month — approximately 4 to 6 blocks monthly
• Tablet salt: approximately 4 to 6kg per person per month in a metered system, more in an inefficient timer-based system

Very hard water areas (300+ ppm) will use more salt than this; softer areas approaching 200 ppm will use less. Your softener should have a salt level indicator — check it monthly and top up before the salt runs out completely. Letting the unit run out of salt for an extended period allows hard water through and can allow the resin to partially lose its capacity.

Tablet salt is available at B&Q, Screwfix, Wickes, and most plumbers' merchants for £8 to £14 per 25kg bag. Buying in bulk — several bags at once — typically reduces the per-bag cost. Amazon and specialist water treatment suppliers online often have competitive prices, particularly on pallet deliveries for households that go through a lot of salt.

Block salt from independent suppliers costs £5 to £10 per two-block pack — meaningfully less than Harvey's own-brand packs. Compatible blocks for Harvey, Kinetico and similar non-electric systems are widely available from plumbing suppliers and online retailers. There is no technical reason to use manufacturer-branded salt if an equivalent-purity alternative is available at lower cost.