Most homeowners think of a water softener as something that runs on its own. That is mostly true on a normal week. A unit that will sit with little or no water use for several weeks needs a short list of checks before you lock the door, and a few more when you get back.
Before you leave
Start with the salt. Look at the brine tank and make sure there is enough salt to get through the trip with some left over. A tank that is low when you return can leave the softener without a full supply of brine for the first regeneration, and that is the cycle that restores the resin.
Next, read the control display. Confirm that the clock shows the correct time and day. If your unit is set to regenerate on a schedule, write down the current setting so you can check it after you return. If it is a metered unit, note the program or capacity setting shown on the label or in the manual.
Then find out what the manufacturer expects for an unoccupied house. Some owners leave the unit in service. Others close the water supply to the softener or use the bypass. Check your owner's manual, or ask the installer which approach fits your model. Do not drain or flush the tank unless the manual or a technician tells you to. Drain steps done at the wrong time can cause trouble that is hard to undo.
If you plan to shut off the main water supply to the whole house, say so in writing to whoever checks the home. Note that the softener is off, and note how to turn the supply back on.
What sitting idle does and does not do
A softener that is not running is not automatically damaged. The resin bed stays in the tank, and the control keeps its program if it has power. The bigger risk is an interruption in the schedule and the salt level, not a sudden failure. That is why the checks above focus on the clock, the salt, and the valve position rather than on opening anything up.
Power is the other thing to think about. If the house will be empty and the power may be cut, ask the installer or the manufacturer what the control does after an outage and whether the clock and program must be set again. Write the answer down.
When you return
Walk to the softener before you turn on the rest of the house. Check that the control shows the right time, that the salt level is adequate, and that the valve position matches what you intended before the trip. Then run cold water at a nearby tap for a short time to clear air and stale water from the lines.
Over the next day or two, watch the water. Notice whether the first regeneration seems to have happened, whether soap lathers normally at the sink, and whether the water feels the way it did before you left. If something seems off, write down what you saw and when, and call a technician with that note in hand.
Keep a note by the unit
Leave a short card near the softener with the date you left, what you set, what you turned off, and who has access. That card is useful for you on the return trip and for anyone who checks the home while you are away.