A softener that runs every day is easy to forget. One that sits idle for several weeks while the house is empty is easier to forget, and the cost of that gap usually shows up after you return. Before you lock the door, decide what the softener should do while no one is drawing water, and write the decision down so whoever checks the house can follow it.
Find out what triggers regeneration
Look at the control head and its settings before you leave. A timer-based unit regenerates on a set schedule whether or not anyone runs a tap, so an empty house still uses salt and water on those cycles. A unit that regenerates based on water use only starts a cycle after a set amount of water has passed through it, so a house with no use may not regenerate at all while you are away. Check the manual or ask your provider which type you have. Some controls offer a vacation or away setting. If yours does, learn how to turn it on and off, and confirm what it does to the regeneration schedule.
Check the salt and the brine tank
Note the salt level before you go. If the unit is timer-based and will regenerate while you are gone, it will draw down the salt, and a tank that starts low may be empty when you return. Top it up to a sensible level, not to the brim, and use the salt type your provider specified. Make sure the brine tank lid and the area around it are clear so the level can be read without moving anything.
Set the bypass and the main shutoff on purpose
Decide whether the softener stays in service or goes into bypass. Leaving it in service keeps the resin on its normal schedule. Bypass routes water around the tank, so the unit uses no salt or water while it is parked, but the house receives untreated supply for as long as the valve stays that way. A valve left in bypass after a trip is a common reason hard water shows up unexpectedly. Whichever position you choose, label it on a card near the unit. If you shut off the main supply to the house, ask your provider whether a long shutdown calls for any separate step on the softener itself.
Write the handoff
If a neighbor, relative, or house sitter will be in the home, give them one page covering where the unit is, the valve position you left, the salt level you left, what the control display should look like, who to call if the unit shows an error or alarm, and your phone number. Name the person who makes that call. Without a name, the call often never gets made, and a small problem has several days to grow.
Check the unit when you return
Look at the clock first. A power interruption can reset it, and a reset clock can move regeneration to a time you did not choose. Compare the salt level with what you recorded. Confirm the valve is in the position you intended. Then run a cold tap for a short time and notice whether the flow and the water look normal. If anything is off, write down what you saw and when before you call, so the technician or provider has a clear starting point.
For the broader picture of choosing and keeping a softener, the Missouri Water Softener Buyer's Guide walks through each stage in order.