Last reviewed: June 2026 by the Water Softener Quotes editorial team

Head-to-head comparison

Both do the same job. The difference is convenience, cost, and what fits your softener.

Block salt

£4–£5 per 8kg pair

Compact blocks slide straight into the softener. No loose salt to handle. Ideal for under-sink installs where space is tight. Slightly higher cost per kg but cleaner and easier to manage.

  • Easiest to load — just slide in
  • No mess, no dust
  • Compact storage
  • Available in most supermarkets

Tablet salt

£6–£8 per 25kg bag

Compressed pellets poured into a separate brine tank. Cheaper per kg. Need more space for the brine tank. Popular with larger capacity systems and commercial installs.

  • Cheapest per kg of salt
  • 25kg bags last longer
  • Widely available online
  • Needs a brine tank (extra space)

Granular salt

£5–£7 per 25kg bag

Loose crystals that dissolve faster than tablets. Same brine tank setup as tablet. Best for very hard water areas or systems with high regeneration frequency.

  • Fastest dissolve rate
  • Good for very hard water
  • Same price bracket as tablet
  • Can bridge in the tank (needs checking)

Which one should I pick?

Practical decision guide based on your setup.

1

Under-sink install, tight space

Go block salt. No brine tank needed, blocks store flat, and you can grab them from Tesco on the weekly shop.

2

Garage or utility room install, space to spare

Either works, but tablet salt is cheaper long-term. The brine tank sits alongside the softener — just top up every couple of months.

3

Very hard water (300ppm+), heavy usage

Granular salt dissolves fastest and keeps up with high-frequency regeneration. Costs about the same as tablet. Ask your installer.

Your installer will advise. Get matched with a vetted local professional who’ll recommend the right salt and system.

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Salt questions

Common questions about water softener salt.

Is block salt or tablet salt cheaper to run?

Tablet salt is typically cheaper per kilogram (around £6-8 per 25kg bag vs £4-5 per 8kg block pair). However, block salt softeners tend to use less salt overall because of more efficient regeneration cycles. The annual cost difference for most households is only £20-40.

Can I switch from tablet salt to block salt?

No — the softener type determines the salt type. Block salt softeners only accept blocks; tablet/granular systems need loose salt. If you want to switch salt type, you would need a different softener unit.

How often do I need to top up salt?

A typical 2-4 bedroom household gets through one pair of 4kg blocks every 4-6 weeks, or one 25kg bag of tablet salt every 6-8 weeks. Larger households or very hard water areas use more. Most softeners have a low-salt indicator.

Where do I buy water softener salt?

Most supermarkets stock block salt (usually near cleaning products). Tablet and granular salt are available from plumbing merchants, Amazon, or direct from brands like Hydrosoft and Cerebos. Some installers offer salt delivery subscriptions.

Does the brand of salt matter?

Not greatly — all water softener salt is high-purity sodium chloride (99.8%+). Stick with recognised brands (Hydrosoft, Cerebos, Harvey) to avoid impurities that could clog the resin. Avoid dishwasher salt or road salt — they contain additives that damage softeners.

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