A point-of-use unit sits under the kitchen sink and treats only the water for one tap. It suits a single person, a couple, or a small household that wants clean drinking and cooking water without treating the whole house. In a rented kitchen the limiting factor is usually the cabinet, not the water. Measure first, then choose.
Start with the cabinet
Measure the width, depth, and height of the space under the sink, and note where the pipes and the garbage disposal sit. Measure to the back wall, to the cabinet door hinges, and to any drawer slide that would be in the way. Then measure the height from the cabinet floor to the underside of the sink basin, because many tanks and filter housings need clearance above them for the cartridge to come out.
Check the door clearance too. A housing that fits the cabinet but blocks the door from closing is a poor fit. Ask whether the cartridge can be changed without lifting the whole unit out.
Check the water connections
Look at the shutoff valves under the sink. Note whether they are compression fittings, quarter-turn valves, or something older. A unit needs a clean cold supply, and the connection method determines which adapters you need. If the valves are stiff or leak when turned, a plumber should look at them before any treatment is added, because a failing shutoff is a bigger problem than the water quality.
Find out where the drain connects. Some systems drain through the sink trap, and some need a separate line. Confirm there is room for the drain tubing without kinking it.
Check the rules before you drill
Many point-of-use systems need a separate faucet, which means drilling a hole in the sink or countertop. In a rental, that is a change to the property. Ask the landlord in writing whether a separate faucet may be installed, who owns the faucet afterward, and whether it must be removed when you move out. A written answer protects both you and the owner.
Match the unit to the household
Estimate how much water the unit will cover. For a single person or a couple, the water used for drinking and cooking is usually a small share of the total. Count the glasses, pots, and coffee made in an ordinary day, then choose a unit whose rated output covers that total with room to spare. Do not buy by the size of the housing alone.
Things to ask before ordering
- Does the unit fit my measured space with the door closed and the cartridge out?
- Which shutoff and tubing fittings do I need, and are they in the box?
- Does the landlord approve a separate faucet in writing?
- How often does the cartridge change, and where is the replacement sold?