Salt is the only consumable your water softener needs to keep working. Understanding which type to use, how much to buy, and when to top up is the difference between a softener that runs perfectly for 15 years and one that causes problems through simple neglect. Here's everything you need to know.
Why does a water softener need salt?
A water softener works by passing your water through a bed of resin beads that capture calcium and magnesium ions — the minerals that cause hardness. Over time, these beads become saturated and need to be refreshed. Salt does this: during the regeneration cycle, a strong brine solution flushes through the resin, displacing the calcium and magnesium and recharging the beads with sodium. The waste water goes to drain; the salt stays in the brine tank, not in your water.
This is an important point worth repeating: the salt is used to recharge the resin, not to soften your water directly. The sodium that ends up in softened water comes from the ion exchange process, not from the salt dissolving into your supply.
The three types of water softener salt
Tablet salt
The most widely used type in the UK. Tablet salt comes in compressed pillow-shaped blocks, typically around 25–30g each, sold in 25kg bags. It's clean, easy to handle, dissolves consistently and works well in the vast majority of domestic softeners including all the units Simply Softeners installs.
Best for: Most households. The default choice for convenience and availability.
Granular salt
Loose crystalline salt, coarser than table salt. Dissolves slightly faster than tablets, which can be useful in high-hardness areas like Sussex where the softener works harder. Some users find granular salt creates slightly more residue in the brine tank over time.
Best for: Higher usage households or very hard water areas. Check your softener manual confirms it's compatible before switching.
Block salt
Large rectangular blocks (typically 4kg each) that sit directly in the brine tank and dissolve slowly over time. Block salt is extremely pure and produces very little insoluble residue, meaning less brine tank cleaning. It's the premium option and works particularly well in eco systems like those installed by Simply Softeners.
Best for: Households that prefer low-maintenance top-ups and want to avoid granular residue. Check your unit's manual — not all softeners accept block salt.
| Salt type | Typical cost per 25kg | Pros | Cons |
|---|---|---|---|
| Tablet | £7–£12 | Widely available, consistent | Can bridge in humid conditions |
| Granular | £8–£13 | Fast dissolving | More residue over time |
| Block (per 4kg block) | £4–£7 | Very pure, low residue | Not compatible with all units |
How much salt does a water softener use?
Salt consumption depends on three factors: your household size, your local water hardness, and whether your softener is metered or timed.
For a typical Sussex household of 4 people in a 300ppm hard water area using an eco-friendly metered softener:
- Approximately one 25kg bag of tablet salt per month
- At a cost of around £7–£12 per bag, that's roughly £84–£144 per year in salt
- An eco metered softener uses up to 50% less salt than a standard timed unit — so the equivalent timed softener would cost £168–£288 per year in salt for the same household
Smaller households (1–2 people) with a compact unit will use considerably less — often just one bag every 6–8 weeks.
Where to buy water softener salt in Sussex
Tablet and granular salt is widely available from:
- B&Q, Wickes, Screwfix — reliable and usually competitively priced
- Costco — excellent bulk pricing if you have membership
- Amazon — convenient with subscription delivery options
- Local plumbers' merchants — often cheaper than DIY chains for larger quantities
Block salt is less universally available in stores — Amazon and specialist water treatment suppliers are usually the most practical source.
How to top up the salt correctly
Most softeners have a brine tank with a lid — typically the larger of the two chambers in a cabinet unit. Simply lift the lid, check the salt level, and top up to roughly two-thirds full. Overfilling isn't harmful but can make the lid difficult to close and increases the risk of salt bridging in humid conditions.
Check the level roughly once a month — most households find topping up every 4–6 weeks is a comfortable routine. Some softeners have low-salt indicators or lights; if yours does, don't let it run empty for extended periods as this will allow hard water to pass through untreated.
Salt bridging: Occasionally, particularly in humid environments like kitchens, salt can form a hardened crust (a "bridge") above the water level in the brine tank that prevents the salt below from dissolving. If your water starts feeling hard again, check for a bridge by pressing gently on the salt surface. Breaking up any crust with a wooden spoon resolves the issue immediately.
Does the salt brand matter?
For tablet salt, not significantly. All reputable UK brands meet the same purity standards. Avoid very cheap or unbranded salt from unknown suppliers as impurities can cause brine tank residue and potentially damage the valve over time. Sticking to recognised brands (BWT, Tesco, B&Q own-brand, Halite) is the safest approach.
Questions about running your water softener?
Simply Softeners provides ongoing support for all our installations across Sussex. Whether it's salt queries, maintenance questions or anything else — we're here.
Get in Touch Call 07788 133 336