You close on a house and find a water softener, a filter housing, a reverse osmosis unit, or a UV lamp already in place. The question is not whether the equipment looks fine. It is whether you own it, whether it still does its job, and who will service it after you move in. Settle those three things before you rely on the system or disconnect it.

Identify what is actually installed

Walk the equipment and write down each unit's type, its location, and the brand and model printed on its label. Note whether the setup is a softener, a sediment or carbon filter, a reverse osmosis unit, a UV lamp, or several in sequence. Find the bypass valve, see whether each unit sits on the main line or at a single faucet, and trace where the drain line goes. A label you cannot read is a question for the seller, not a reason to guess.

Ask who owns it

Ask this in writing, through your agent if you have one: is the system owned outright, or is it leased or rented from a water company? Rented equipment usually stays with the rental company, and the seller may still owe payments or a return visit. Ask for the contract, not a verbal answer. Read the transfer terms, the cancellation terms, and any fee that applies when the property changes hands.

Ask for the service history

Ask who last serviced the system and what was done. Request the service receipts or invoices. Ask whether the installer still operates in the area and whether the model's replacement media or cartridges are still sold. If parts are no longer available, a routine replacement becomes a larger job, and that changes the keep-or-replace decision.

Test the water before you decide

Ask the seller for any recent water test results they have. Then plan your own test at the kitchen tap, drawing one sample before the treatment and one after it if the equipment allows. A test describes the water at the moment it was taken, so one result is a starting point, not a verdict. Compare the results to the problem the system was installed to solve. If the system is not addressing that problem, you have a reason to replace or remove it regardless of its condition.

Check that it runs and is sound

Look for leaks at every fitting and valve, staining or moisture on the floor beneath the unit, and a clear, unobstructed drain. For a softener, check the salt level and confirm the unit can complete a regeneration cycle when you or a technician run it. For filters, check the pressure gauge if one is installed and note the housing condition. Turn the bypass valve to confirm it moves freely. Do not run any unit whose connections you have not inspected.

Decide: keep, replace, or remove

Keep the equipment if you own it, it runs properly, your test shows it treats the problem you have, service and parts are available, and you know roughly what recurring upkeep involves. Replace it if you own it but it is failing or no longer matches your water. Remove it if it is rented and the company wants it back, or if it treats a problem your water does not have. Removal requires a bypass plan first. Do not disconnect plumbing until you know how water will reach your fixtures afterward.

Price the upkeep, not just the unit

Ask the company you would hire, or the one that serviced the system, for the full recurring list: salt, cartridges, media, and service visits. Ask how often each is needed and get the schedule in writing. A system that is free to inherit can still cost more over time than a replacement, so compare the upkeep on paper before deciding.

Confirm what stays with the house

Ask your agent or closing contact to confirm in writing which water equipment conveys with the property and which is leased, rented, or excluded. A verbal statement that the system stays is not enough, especially when the equipment is rented or tied to a service contract.

If you need an assessment

When you contact a local company, ask whether it will evaluate equipment it did not install, what a service visit covers, whether it will take over service of an existing system, and what it needs to see before quoting. Ask it to put the answers in writing. To find companies that have been recognized for serving greater St. Louis, start with the Best Water Companies STL award winners, then compare each company's answers against the same questions.