Introduction
Salt is the consumable that keeps a water softener working. Without it, the ion-exchange resin inside the unit loses its ability to remove calcium and magnesium from your water, and within a few days you are back to hard water. Getting the right type — and keeping the salt topped up — is one of the few ongoing maintenance tasks a water softener owner actually has.
This guide explains the difference between block, tablet and granule salt, which systems use which, how much you will get through, and what it costs.
Block Salt
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 (Pillow Salt)
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
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.
How Much Salt Will You Use?
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.
Where to Buy Water Softener Salt Cheaply
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.
Frequently Asked Questions
Harvey softeners use block salt — rectangular compressed blocks sold in pairs. Harvey sells their own proprietary curve salt blocks, but compatible blocks from independent suppliers work equally well and cost significantly less. A standard pair from an independent supplier costs around £5 to £10 versus £15 to £25 for Harvey-branded packs.
No — you need to use the salt type your specific softener is designed for. Block salt for non-electric twin-cylinder systems like Harvey and Kinetico; tablet salt for most single-tank electric systems. Using the wrong type will not destroy the unit but can cause operational issues. Check your manual or the manufacturer's website to confirm which type your system requires.
Check the salt level monthly. Most households need to top up every 4 to 6 weeks depending on water hardness and water usage. Your softener should have a salt level indicator. Do not let it run out completely — a few days without salt allows hard water through and the resin gradually loses capacity.
Tablet salt at B&Q, Screwfix, or Wickes is typically £8 to £14 per 25kg bag. Buying in multi-bag quantities reduces the cost. For block salt, independent online suppliers and plumbing merchants offer compatible blocks at £5 to £10 per pair — cheaper than manufacturer-branded versions. Amazon also carries competitive prices on both types.
Hard water passes through the softener and into your home. If the unit runs dry for more than a few days, the resin loses some of its softening capacity and needs to regenerate properly once salt is restored. Top up promptly and run a manual regeneration cycle if your unit supports it. Short periods without salt are not catastrophic but habitual neglect of salt levels reduces the softener's performance.
Conclusion
The right salt is whichever type your softener is designed for — block for non-electric twin-cylinder units like Harvey and Kinetico, tablet for most single-tank electric systems. Where you buy it matters considerably for cost: independent suppliers charge a fraction of what manufacturer-branded salt costs for equivalent purity.
Keep the level topped up, check monthly, and buy in bulk to reduce the per-unit cost. Salt is the only regular consumable a water softener needs.
Written by water-softener-quotes · Content Team