The installer's last hour on site is the cheapest time to find a problem. The crew is still in the driveway, the tools are still out, and the fix is usually a fitting or a setting rather than a return visit. Once the crew packs up, every open question becomes a phone call, and a phone call is easier to put off. A short walkthrough before anyone signs the completion form protects you from that.
Ask for the install record before you start
Ask the crew lead for a written install record that lists the make, model, and serial number of each unit, the date it went in, the cartridge or media type, and the settings the technician programmed. If the company does not keep this sheet, ask them to fill one out on the spot. You will need these details the first time anything goes wrong, and most people cannot reconstruct them later.
Find the bypass and make them show it to you
Ask the technician to point to the bypass valve and to demonstrate both positions: normal service and bypass. Then do it yourself once while they watch. Confirm that the handle position is clearly marked, that you can reach it without moving other equipment, and that the water comes out of the tap as expected in each position. A bypass that is set wrong or left open is one of the most common ways a system quietly stops treating water, and the walkthrough is the moment to catch it.
Locate every shutoff and label it
Make sure you can find and close the main shutoff for the house, the inlet and outlet valves for the new equipment, and any drain valve. Ask whether each one is labeled. If a valve is hidden behind a panel or a cabinet door, ask whether it can be relocated or at least marked with a tag that someone else in the house can understand.
Run water and check every joint
Open a cold tap downstream of the system and let it run while the technician watches the flow. Look for sputtering, which usually means trapped air, and for any drip at a fitting. Then wipe each joint dry with a paper towel and check it again after the crew has been gone for a while, because some leaks only show once the system is pressurized and stable. Ask the technician how long they will watch the system before they consider it stable, and whether they will come back if a joint weeps later.
Record the pressure and the settings
Ask for the pressure reading, where it was taken, and the operating range that the manufacturer lists in the manual. The reading alone means little unless you can compare it to that range. For a softener, write down the hardness setting, the regeneration schedule or trigger, the salt level, and the time of day it is set to regenerate. For a filter, confirm the cartridge type and the replacement interval, and ask that the interval be written on the housing or on a card attached to it. For a UV unit, ask where the lamp replacement reminder is kept and who will set it. Photograph the settings screen or the card so you have a record that does not depend on memory.
Check the drain and the power
If the system discharges backwash or brine, confirm where that water goes and that the discharge line is secured, free of kinks, and not sitting in a place where it could back up. Confirm the power source for the unit, whether it is on a dedicated outlet, and whether anything in the setup will be affected if the outlet is switched off. Ask what the system does during a power interruption and whether it needs to be reset, and write the answer down.
Collect the paperwork and the contact path
Before the crew leaves, make sure you have the owner's manual, the warranty card or registration form, the install record, and the service contact for the company. Ask the company to tell you the first person to call for a problem, what the response path is after hours, and whether the warranty requires registration within a set window. If any of these items are missing, make a list and ask the company to deliver them in writing.
Write the punch list before you sign
If the walkthrough turns up anything unfinished, write it on the completion form or on a separate sheet, with the item, who will fix it, and how you will confirm it is done. Do not sign a blank completion form or a form that says the work is complete if you have open items. Signing a completion form usually starts the warranty clock, moves final payment forward, or both, so read what the signature commits you to. If you are not sure what a line means, ask the crew lead to explain it and write the explanation in the margin.