A water softener, filter or reverse osmosis unit in a house you are buying is a working system you did not choose and may not understand yet. Before closing, your job is to find out whether you own the equipment, what condition it is in, what paperwork goes with it, and what maintenance it needs next.
Find out whether you own the equipment
Some systems are leased or rented from a provider rather than purchased. A rental unit may stay with the provider when the house sells, and the monthly charge may continue under the seller's account. Ask the seller directly whether any water treatment equipment is leased, financed or under a service agreement, and ask for the name of the provider. If the answer is yes, read the agreement to see whether it transfers to a new owner, what the buyout or removal terms are, and who pays to cancel. Your purchase contract should also say what conveys with the property. Ask your agent or attorney to confirm the equipment is listed there if you plan to keep it.
Record what is installed
Write down the brand, model and serial number of each unit, plus the install date if the seller knows it. Check the label on the tank or cabinet, because the model name on a paper invoice may not match what is physically in the basement. These details decide which warranty applies, which filters or media fit, and whether a provider can find the unit's records later.
Ask for the warranty and service paperwork
Ask whether the unit was registered with the manufacturer and whether the warranty is still open. Registration and transfer rules vary by manufacturer, so request the written terms rather than relying on the seller's description. Ask for the installation invoice, any service visit records, and the date of the last filter, media or cartridge change. Gaps in the record are useful information: they show how much attention the system has had and how much work you may need to do soon.
Check the water results you are relying on
A water test done for a previous owner describes the water at that time, not necessarily the water today. If the seller provides a test, check its date, what it measured and where the sample came from. A test from a neighboring address does not describe your house. If water quality matters to your decision, arrange your own test during the inspection window, using a lab or provider that will explain the results in writing.
Walk the system during your inspection
Ask the seller to run water at a few taps while you watch the equipment. Look for dripping fittings, damp floors around the tank or cabinet, and a bypass valve set where the seller says it should be. Note whether the unit is powered on, whether a display or indicator shows a fault, and whether salt or replacement cartridges are on hand. Your inspector can check the water heater and plumbing, but tell them about the treatment system so it is included in the report.
Plan the first year
Before closing, list what the system will need in the next twelve months: salt deliveries, cartridge changes, a service visit, or a water test. Confirm which of these the seller has been paying for and whether a maintenance agreement is active. If you want to keep the provider the seller used, ask whether it will honor the account under your name. If you plan to switch, have the model and serial information ready when you call.
What to bring to closing
Keep copies of the equipment list, warranty terms, service records, any rental or maintenance agreement, and the water test if one exists. File them with the rest of your house papers. You will need them the first time something stops working, and the seller will not be available to explain them later.