If you have moved into a hard-water area or limescale has returned to your kettle, the brine tank is a sensible place to start. Choosing salt is mostly a matter of matching the format to your softener, then checking the tank regularly. One UK point is also worth knowing: guidance recommends keeping at least one tap, normally the kitchen cold tap, on an unsoftened supply for drinking and cooking.
The quick answer: match the salt to your softener
Your softener’s design determines the salt format. A machine built for blocks may not work correctly with tablets, while fine crystals can cause problems in a tank designed for pellets. Before changing formats, read the manual or contact the manufacturer’s support team. Compatibility can vary between models from the same brand.
Common pairings in UK homes include:
- Compact twin-cylinder units fitted under a kitchen sink often use block salt.
- Many single-tank electric or metered units use tablet or pellet salt.
- Some older units use granular salt, but you should confirm this before filling the tank.
Potassium chloride (KCl) is another option for some households. However, it costs more than sodium chloride, and some softeners require reprogramming for KCl. You must confirm compatibility with your manufacturer before switching.
Salt types explained
Block salt
Blocks are dense, moulded slabs made for particular compact softeners. They are tidy to handle, produce little spillage and make it easy to see how much salt remains. Packs often contain two individually wrapped blocks, although sizes vary. The main limitation is compatibility: only use blocks in a machine designed for them. Some Harvey softeners use model-specific block salt, so owners should follow the instructions supplied with their unit.
Tablet or pellet salt
Tablets are compressed pellets and are widely used in single-tank softeners. Pure dried vacuum (PDV) or evaporated salt is common because it usually contains fewer insoluble impurities than lower-grade alternatives. Pellets also tend to dissolve more consistently than very fine crystals. Check the bag for its intended use, purity and relevant quality standard.
Granular salt
Granular or crystal salt is a coarse, loose format suitable for certain softeners. If the grains are too fine for your machine, they can form a slushy layer at the bottom of the tank and prevent the salt from dissolving evenly. Some solar salt also contains more insoluble material than evaporated pellets, which may lead to more frequent cleaning. Do not assume granular dishwasher salt is suitable for a water softener.
How hard is your water?
UK water hardness is commonly expressed in milligrams per litre (mg/L) of calcium carbonate. The Drinking Water Inspectorate describes water containing 200 to 300 mg/L as hard and water above 300 mg/L as very hard.
You do not need to estimate your home’s figure from the kettle scale alone. Ask your water company for a water quality report or use its online postcode checker. Knowing the local hardness helps you confirm whether a softener is useful and ensures the unit is set to regenerate at an appropriate interval.
Care and safety for your brine tank
Salt choice matters, but routine maintenance is just as important. Check the tank occasionally rather than waiting for softened water to stop. Practical plumbing maintenance tips can also help you spot damp cupboards, ageing valves and small leaks around an under-sink installation.
How much salt to add
Keep the tank around half full unless your manual specifies another level. Check it every four to six weeks and use only salt intended for water softeners. Filling a tank to the top can encourage bridging, especially when the salt is exposed to humidity or remains unused for long periods.
Spotting and fixing bridging or mushing
A salt bridge is a hardened crust that leaves an empty space between the salt and the water below. Common signs include a level that does not fall and the return of hard-water symptoms even though the machine appears to regenerate.
Use a blunt handle to break the crust gently without striking the tank walls or internal brine tube. Run a manual regeneration if the instructions recommend it, then check the tank again after the next cycle. If sludge repeatedly forms at the bottom, confirm that you are using the correct format and consider a higher-purity product.
When to clean the tank
Inspect the bottom of the tank whenever the salt level is low. If you see sediment or compacted residue, remove the remaining salt and clean the tank according to the manual. Some manufacturers recommend warm soapy water followed by thorough rinsing, while others provide specific sanitising instructions. Do not use unapproved household chemicals. When ordering a replacement, choose water softener salt in the format specified by your manual.
UK standards and health notes
For domestic base-exchange softeners, UK guidance recommends retaining an unsoftened outlet for drinking and cooking. This is why installers commonly leave the kitchen cold tap connected to the hard-water supply. The UK drinking-water limit for sodium at consumers’ taps is 200 mg/L. If you have been advised to follow a restricted-sodium diet, ask a healthcare professional whether softened water is suitable for you.
Packaging may refer to BS EN 973, the standard covering sodium chloride used to regenerate ion-exchange equipment for drinking-water treatment. Check that the product is intended for water softeners and read any stated grade or class. Harvey is among the UK suppliers that reference BS EN 973 on suitable salt products, but compatibility with the individual softener remains the first consideration.
Where to buy and what to check
Supermarkets, plumbers’ merchants, manufacturers and online retailers sell water softener salt. The practical differences are format, purity, pack size and delivery cost. Never use road salt or ordinary table salt in a brine tank. Dishwasher salt should also be avoided unless the softener manufacturer explicitly approves that exact product.
Online suppliers stock block, tablet and granular formats for different machines. Harvey, for example, offers Grade A block salt associated with BS EN 973 for compatible models. Treat any manufacturer’s description as product information to compare with your manual, not as proof that the salt suits every softener.
Before buying, check the following:
- Confirm the format and pack size specified for your softener.
- Check that the salt is intended for regenerating water softeners.
- Look for BS EN 973 and review the stated purity or grade.
- Choose PDV or evaporated salt if insoluble residue has been a problem.
- Compare the price per kilogram and include delivery charges.
Subscription deliveries can be convenient, but choose an interval based on actual household use. Water hardness, water consumption and regeneration settings all affect how quickly the tank empties.
Your first refill, step by step
- Check the manual for the required salt type and refill procedure.
- Open the lid and inspect the tank for bridging, sludge or unusual water levels.
- Add the correct salt without exceeding the manufacturer’s fill line.
- Close the lid and run or schedule regeneration if the instructions require it.
- Check the level again in four to six weeks.
Conclusion
Start with the softener manual, choose the specified format and use salt made for regeneration equipment. Keep the tank near the recommended level, inspect it every month or so and deal with crust or residue before it affects performance. Occasional cleaning and an unsoftened kitchen tap will help the system operate reliably while following UK guidance.
FAQs
Can I mix tablet and block salt?
Generally, no. Brine tanks are designed around a particular salt shape and dissolving rate. Mixing formats can produce uneven brine or contribute to blockages. Check the manual or ask the manufacturer before changing salt.
Is potassium chloride better than sodium chloride?
It is different rather than universally better. Potassium chloride may suit compatible systems when a household wants to limit added sodium, but it costs more and may require a setting change. Discuss dietary concerns with a healthcare professional.
How often should I top up the salt?
Check the tank every four to six weeks and refill it according to the manual. Consumption depends on water hardness, household water use, softener capacity and regeneration frequency.
What happens if the softener runs out of salt?
Without salt, the resin cannot regenerate effectively, so hard water begins passing through the system. Refill the tank with the correct format and follow the manual’s regeneration procedure. Normal softening should return once the unit has completed a successful cycle.
