A water softener runs for years without much attention, which is exactly why its history tends to vanish when a house changes hands or a tenant moves out. The next person inherits a tank full of resin, a valve with unknown settings, and a warranty nobody can find. A short written handoff prevents most of the confusion, and it takes less than an hour to assemble if you start before the move.
Gather the identity details first
Look at the label on the control valve and the tank. Write down the manufacturer, model, and serial number exactly as printed. These are what a service tech or parts supplier will ask for, and they are what decide whether a replacement part can still be ordered. If the label is worn, photograph it in good light and keep the photo with the file.
Collect the paperwork that proves what was done
Put these in one folder, paper or digital:
The owner's manual, or a link to the manufacturer's copy of it. The warranty card or the confirmation that the warranty was registered, along with the warranty terms. The installer's name, company, and phone number. Any permit paperwork or inspection sign-off for the install. Every service invoice, salt receipt, and parts receipt you have kept. If you do not have a record of a service visit, say so in the file rather than leaving a gap that looks like neglect.
Write down the current settings
Settings drift over time, and the next owner will not know what you changed. Record the hardness setting the unit is programmed for, the regeneration schedule or trigger, the salt dose setting if the model has one, and the time of day regeneration runs. Note the last water hardness result you measured, where and how you measured it, and the date of that test as a plain note in the file. Make clear whether the settings were set by you or by a technician, since that tells the next person whom to ask.
Mark the shutoffs and the bypass
Label the main water shutoff, the softener's inlet and outlet valves, and the bypass position. Add a short note on which position means softened water and which means bypassed water. A buyer or tenant who cannot find the bypass during a leak is the most common reason a softener gets damaged while it sits unattended. Note where the drain line discharges, because a drain that backs up is easy to miss.
Name the people who do the recurring work
Write down who orders salt, who tops up the brine tank, who handles any service plan, and whom to call for repairs. If you rent the home, name who owns the softener, since a landlord may own it while a tenant pays for salt, or the reverse. Check your rental or sale agreement for what it says about fixtures and equipment, and ask whether any service plan or warranty transfers to a new owner and what that transfer requires. Those terms vary, so read the actual paper rather than assuming.
Hand it over in person
Walk the new owner or tenant through the bypass, the salt tank, and the settings while you are still there. Give them the folder and tell them where the key records are. A five-minute walk-through with the paperwork in hand usually prevents months of guesswork, and it gives you a clear record that the unit was in working order when you left.