A new water treatment unit usually goes in with a few hours of work at the connections, and most of the problems that show up later start there. A fitting that was not fully seated can seep for a day before it drips onto a cabinet floor. The useful moment to catch it is install day, while the installer is still in the house and the joints are still exposed. This guide covers what to check at each connection and what to ask before the crew leaves.

Know which connections were made

Before you look at anything, ask the installer to point out every place the water system was opened and rejoined. Usually that means the cold supply tie-in, the inlet and outlet of the treatment unit or bypass valve, the drain connection if the unit makes drain water, and any fitting on a tank, housing, or cartridge head. Ask what type of fitting each one is: a push-fit, a compression fitting, a threaded joint, or a soldered joint. The type tells you what a good seal looks like and what kind of seepage to expect if one fails. A push-fit should show the tube fully seated past the collet, and a compression fitting should be snug with no gap at the nut.

Restore pressure slowly and watch

Water pressure is often the first real test. Ask the installer to bring the supply back slowly rather than opening the main all at once, which can push a marginal fitting to fail. Once the system is pressurized, leave the house in normal use for a set period while someone watches the work. Dry joints can look fine for a minute and wet within the hour, so the watch should run long enough to matter. Pay attention to the area under the sink, behind the unit, at the bypass valve handles, and along the floor beneath any tank or housing.

Check the drain path as carefully as the supply

If the unit discharges water, the drain line is a second place for leaks. Run the unit through a normal cycle or flush if the installer can do so safely, and watch the drain connection and the hose or tubing from start to finish. Look for water at the joint where the line meets the drain, at any clamp or adapter, and at the low point of the line. A drain that drips only during the discharge cycle is still a leak, and it is easier to fix now than after the cabinet is closed.

Ask for photos before anything is covered

If the connections will be hidden behind a cabinet panel, a wall board, or a finished floor, ask for photos of each joint before the covering goes back on. Photos taken on install day are useful later if a weep appears, because they show how the fitting was made and which way the tube or hose runs. Ask the installer to note which fittings were made with push-fit, compression, or soldered joints. Keep the photos with the rest of the paperwork for the system.

If you find a weep

A small weep on install day is common and usually fixable on the spot. Do not accept a plan to check it later without a date. Mark the location, ask the installer to tighten or remake the joint while the crew is still there, and then run the system again for a short period to confirm the fix holds. If a joint keeps weeping, shut off the supply to the unit at its valve rather than letting it run overnight, and ask the installer to come back before you turn the supply on again. Write down what you saw, what was done, and who did it.

Before you sign off on the work

When the crew says the job is done, ask them to confirm that every connection you identified was checked under pressure, that any weep you saw has been fixed and retested, and that the drain path was watched through a cycle. If you are unsure about a joint, ask the installer to show it to you again before they leave. A short walk through the connections at this point costs little and gives you a clear starting record if anything changes in the first few days.