Block salt is clean, light to handle and suits compact cabinet softeners; tablet salt is generally cheaper per kilogram, works in a wider range of machines, and comes in heavy sacks. The choice is usually determined by which machine you have.
They are the same chemical
Both are sodium chloride at high purity, manufactured specifically for water treatment. Neither softens better than the other, neither regenerates the resin more thoroughly, and neither produces different water. Any claim otherwise is marketing.
What differs is the physical form, and that drives everything practical about living with a softener.
Block salt
- Comes as two moulded blocks, typically handled as a pair and dropped into the machine.
- Clean. No dust, no residue, no scoop. You handle a block and that is it.
- Light to lift individually, which matters considerably for anyone who would struggle with a 25 kilogram sack.
- Suits compact cabinet softeners, which are designed around block dimensions and are often the only thing that fits under a kitchen sink.
- Cannot bridge. Because the blocks dissolve from the bottom in a shallow brine well, there is no crust-over-void failure mode.
- Generally more expensive per kilogram, sometimes noticeably.
- Only works in machines designed for it. You cannot put blocks into a tablet machine.
Tablet salt
- Comes as compressed tablets in sacks, typically 10 or 25 kilograms.
- Generally cheaper per kilogram, particularly bought in quantity.
- Works in most conventional softeners with a brine cabinet.
- Widely available – builders’ merchants, agricultural suppliers, and online in pallet quantities.
- Heavy to handle. A 25 kilogram sack is a real lift, and it has to be carried to wherever the softener is.
- Can bridge. In a damp environment the tablets can fuse into a crust across the tank with a void underneath, and the machine then stops softening silently.
- Needs a machine with a brine cabinet, which is generally a larger unit.
If the tank looks full but the salt level never seems to go down, push a broom handle gently down through the salt. If it breaks through a crust into a void, you have a bridge and the machine has not been regenerating properly – possibly for weeks. Break it up, and consider whether the softener is somewhere too damp.
Which to choose
In practice the machine decides, not you. Block salt machines take blocks; tablet machines take tablets. So the decision is really made when the softener is chosen, and these are the considerations at that point:
| If… | Lean towards |
|---|---|
| Space is tight – under a kitchen sink | Block. Compact cabinet machines are designed around it |
| The softener will be in a garage or utility with room | Tablet. Cheaper running cost and the space exists |
| Whoever loads it cannot lift 25 kg | Block, without question |
| The softener is somewhere damp | Block – no bridging risk |
| Lowest running cost matters most | Tablet, bought in quantity |
| The softener will be loaded rarely by somebody else | Block. Simpler and cleaner for anyone unfamiliar |
| Rural property, buying in bulk is easy | Tablet. Agricultural suppliers stock it by the pallet |
For a lot of Norfolk properties with a garage or utility room, tablet salt bought in quantity is the sensible answer. For a kitchen-cupboard installation in a smaller house, block is frequently the only thing that fits.
What not to use
- Table salt or cooking salt. Contains anti-caking agents and other additives that will foul the resin. Never.
- Dishwasher salt. Different purity and grain specification, and expensive for the quantity a softener uses.
- Rock salt or de-icing salt. Full of insoluble material that will clog the brine system.
- Granular salt in a machine specified for tablets, or vice versa, without checking. Grain size affects how the brine well behaves.
Use salt sold specifically for water softeners, to the appropriate standard. It is not expensive relative to the damage the wrong thing does.
Storage and handling
- Keep it dry. Damp salt cakes, and caked salt bridges. A sack stored on a concrete garage floor will draw moisture – put it on a pallet or a shelf.
- Do not overfill the tank. Leaving headroom reduces bridging and makes it easier to see the level.
- Check the level monthly rather than waiting for the water to feel hard again. By the time you notice the difference, the machine has been regenerating poorly for a while.
- Keep the lid on to stop dust and debris getting in.
- Do not let it run completely empty. A regeneration with no salt achieves nothing and the resin stays exhausted until the next cycle.
Softener not performing? Check the salt level and check for a bridge before assuming anything is wrong with the machine.
Questions we get asked about this
Is block salt better than tablet salt?
Chemically they are identical. Block is cleaner and easier to handle and cannot bridge; tablet is generally cheaper per kilogram. Neither softens better.
Can I put tablet salt in a block salt machine?
No. Block salt machines have a shallow brine well shaped for the blocks and there is nowhere for tablets to sit correctly. Use what the machine is designed for.
How much salt should a softener use?
It depends on your water hardness, how much water you use, and whether the machine is metered. A metered unit regenerates only when the resin is exhausted, which uses substantially less than a timer-based one.
Why is my salt not going down?
Most likely a salt bridge – a crust over a void, so the water is not in contact with salt. Push gently down through it with a broom handle. If it breaks through, you have found the problem.
Can I use dishwasher salt?
You could, but it is a different grain specification and it is expensive for the quantity a softener consumes. Use salt made for water softeners.
Where should I store the salt?
Somewhere dry and off a concrete floor. Damp salt cakes, and caked salt is what bridges.
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.