If you are buying a home that already has a water treatment system, or selling one, the most useful thing to hand over is not the equipment itself. It is the paper trail that shows how the system was installed, how it was set up, and what has been done to it since. Without that record, the next owner inherits a tank and a control head they cannot read, and every service call starts from zero.
Request the documents while the sale is still open
Ask the seller, or the provider named on the paperwork, for these items before closing:
Installation paperwork: the invoice, the installer's name and phone number, and the model and serial number printed on the unit. The serial number matters because manufacturers and parts suppliers usually identify components by it, not by the house address.
The owner's manual and any setup sheet showing the programmed settings, such as hardness setting, flow rate, and cycle or backwash timing, along with the media or cartridge type.
Service and maintenance records: dates of media changes, cartridge swaps, and any repairs, plus notes on which parts were replaced. Replaced parts tell you what is original and what is not.
Water test results, if any exist, with the name of the lab and the items that were tested.
Any permit or inspection record for the installation, if the local building office required one. Ask that office what it keeps on file, since some jurisdictions have records the seller never saw.
Warranty registration and any active coverage, including the expiration date.
Any service agreement, and whether it can pass to a new owner or ends at the sale.
If the seller cannot produce some of these, that gap is useful information. Ask why the records are missing and whether the previous provider still keeps them on file.
Confirm what transfers and what does not
Warranties often belong to the original purchaser and may not follow the house. Some require the new owner to register the equipment within a set window, and missing that step can end coverage. Read the warranty for its transfer clause, and do not assume it carries over because the system is bolted to the house.
Find out whether the equipment is owned or leased. A rented unit stays the property of the company that installed it, so the agreement, removal terms, and service route belong to that company, not to the house. Confirm the ownership status in writing before closing so you are not surprised by a removal request after you move in.
Service agreements follow the same logic. Ask the seller or the provider to confirm in writing what happens to the agreement at sale, including whether it can be assigned, paused, or cancelled, and what notice is required.
Check the system with the new owner present
Before you rely on the handoff, walk through the system with the seller or the outgoing provider if possible. Compare the settings on the control head with the manual, confirm that any consumables such as salt, cartridges, or media are at the level the setup sheet describes, and look for any warning messages. Write the date, the settings, and the readings in your own log. That entry becomes the baseline for the next person who owns the house, and it shows you what was normal on the day you took over.
Keep the file with the house
Gather the records into one folder, paper or digital, and put the model and serial number on the cover page. Add the warranty expiration date, the name and phone number of the last provider who serviced the system, and a short note of when consumables were last changed. Keep the file where the next owner can find it, such as with the house closing documents or the appliance manuals. A clear packet is the most practical gift you can leave, because it lets the next provider understand the equipment quickly and keeps the system running without guesswork.