Every treatment unit should have a shutoff valve on the inlet side and another on the outlet side, so you can close off the unit without shutting the whole house. Most owners never touch these valves until something goes wrong. When that day comes, a valve that will not close fully, or one that drips when closed, turns a five-minute cartridge change into a wet-floor emergency. Before you decide who does the work, find out what you actually have.

Find out what kind of valve you have

Look at the handle or stem and note how it moves. A ball valve has a lever or a quarter-turn handle and usually closes in about a quarter turn. A gate valve has a round handle that you turn many times, and the stem rises as you turn it. Gate valves are common in older homes and tend to fail in ways ball valves do not. They can stop closing fully, leave a slow seep past the stem, or seize after years without use.

Also note how the valve connects to the pipe. Soldered (sweated) joints need heat and experience to replace. Compression fittings can be undone with wrenches but often need a new ferrule to seal well. Push-to-connect fittings are the easiest for a homeowner to swap, but only if the pipe end is cut square, clean, and undamaged.

Test the valves before you need them

Once a year, or before any filter change, close the inlet valve and then open a cold tap on the downstream side. The flow should stop within a few seconds. If water keeps running, the valve is not sealing. Next, check the stem and packing area for drips while the valve is open. Any moisture there means the packing is failing. Finally, turn the valve back on slowly and watch the fittings for weeping over the next few minutes. Mark the result on the unit's parts record so you have a baseline.

Do not force a stiff gate valve. Old valves can snap at the stem, and a broken valve may leave you with a pipe that cannot be shut at all until the main is turned off. If the handle is hard to move, treat that as the finding and plan the repair rather than testing harder.

What you can reasonably do yourself

A homeowner who can shut off the main, relieve the pressure by opening a tap, and cut pipe square can usually replace a ball valve on a push-to-connect or compression connection. Plan for some water spillage, have towels and a bucket ready, and dry everything thoroughly before reopening the main. Pressurize slowly and check every joint again after an hour.

When the job belongs to a plumber

Hire the work when any of these are true: the valve is soldered and you are not comfortable with torch work near a wall or cabinet; the valve sits on the service line or near the meter, where shutting off the flow may require the utility; the stuck valve is on a line that must stay live while you work; or the leak would run into a wall, ceiling, or finished floor that you cannot easily dry out. Some jurisdictions also require a permit or inspection for changes to supply plumbing, so check local rules before you start.

What to ask before you agree

Ask the plumber which valve type they will install and whether it is full port, so the flow is not restricted. Ask whether the price includes the valves and fittings, not only the labor. If the old valve breaks during removal, ask who pays to repair the pipe and whether that cost is covered in writing. Ask how they will test the new valves under pressure before they leave, and where the new shutoffs will sit so you can reach them in an emergency. A clear answer to each of these tells you whether the quote covers the whole job or only the part that is easy to price.

Decide before the next filter change

If your valves close fully, do not drip, and move freely, you have time and can plan the next filter change with confidence. If they fail the test, make the call now rather than during an emergency. Replacing a valve on a calm day, with the right tools and a clear plan, is far cheaper in water damage and stress than finding out the valve is dead while the filter housing is open.