There is no single answer to how often a softener needs salt, and anyone who gives you one is guessing. Consumption is set by three things that differ in every house, and the useful habit is not a schedule but a check: look at the tank on a regular day of the month and learn your own interval, which then becomes a diagnostic in its own right.
What sets your consumption
Three things multiply together. How hard the incoming water is, since every unit of hardness removed has to be flushed out with brine. How much water the household actually uses, because the unit regenerates on volume treated. And how much salt per regeneration the valve has been programmed to draw, which is a setting rather than a fixed property. A high efficiency setting on moderately hard water can look almost static next to a large family on very hard well water using the same size unit.
The level to keep
Keep the tank at least a third full and do not fill it to the brim. A tank filled to the top is more likely to form a salt bridge, a solid crust spanning the tank with an empty space beneath it, which leaves the brine well drawing from nothing while the tank looks full. Leave a hand's width of space above the salt. Check that the salt is loose rather than crusted when you top up, and break any crust with a broom handle before adding more on top of it.
Use the level as a diagnostic
Mark the salt level with a marker and note the date. If the level stops falling, the softener has stopped drawing brine, and the causes are a salt bridge, a blocked injector, a stuck valve or a restricted drain. If it starts falling much faster than usual, something has changed: a leak on the softened line, a valve regenerating too often, or a household using far more water. Either way the tank is telling you something before the water quality does, which is why the habit is worth keeping.
Salt type and storage
Clean pellets dissolve with little residue. Rock salt carries insoluble grit that settles in the bottom of the tank and eventually reaches the injector screen, which is where most blockages start. Potassium chloride can be used instead of sodium chloride and generally consumes more per regeneration. Store bags somewhere dry, because damp salt cakes and is harder to break up. Our salt delivery guide covers standing orders for households that would rather not carry bags.
Questions people ask about how often to add salt to water softener
How often should I add salt?
There is no universal interval. Learn yours by marking the level and noting the date, then top up before it falls below about a third full.
Should I fill the tank to the top?
No. A brim full tank is more prone to salt bridging, which leaves the brine well drawing from an empty space under a solid crust.
The salt level has stopped falling. What does that mean?
The softener has stopped drawing brine: a salt bridge, a blocked injector, a stuck valve or a restricted drain line.
Does the type of salt matter?
Clean pellets leave little residue. Rock salt carries grit that settles and eventually reaches the injector screen, where blockages start.