An older house in St. Louis often has a kitchen sink that was never planned for a second faucet, a filter housing, or a storage tank. Before you buy any equipment, the sink spot itself deserves a careful look. A good location makes the install easier, keeps service simple, and avoids cabinet damage later. This guide walks through what to check in an older home before you choose where the system goes.
Start with the cabinet and what is already under it
Open the cabinet doors and take everything out. Look at the supply lines, the shutoff valves, the drain trap, and the garbage disposal if there is one. Note where the cold water line enters the cabinet, because a reverse osmosis feed usually taps that line. Check whether the supply line is copper, braided steel, or older flexible tubing, and whether the shutoff valve turns freely. A valve that is stiff or weeps should be looked at by a licensed plumber before any new connection is made.
Measure the open space inside the cabinet from front to back and from side to side. Include the area where the doors swing, since that often limits how far a storage tank can sit. Many older cabinets were built around a basic sink trap and nothing more, so the room left over may be smaller than it looks.
Check the floor and the cabinet base
Older St. Louis homes sometimes have cabinet bottoms that have softened from years of small drips. Press on the floor of the cabinet near the back wall and near the sink drain. If the wood gives, feels spongy, or shows dark staining, fix that first. A storage tank full of water is heavy, and a weak base will not hold it safely.
Look at the wall behind the cabinet too. Plaster and lath walls may not have solid backing for mounted parts. If you plan to mount a filter housing or bracket on the wall, find the studs with a stud finder and confirm the mounting points before drilling.
Plan for the drain and the air gap
Most reverse osmosis systems send wastewater to the drain, and many local codes call for an air gap or a similar backflow device at the sink. Look at the sink deck to see whether there is an open hole for a dedicated faucet or air gap fitting. If the sink has no spare hole, the layout changes, and you may need a different faucet arrangement. Ask your plumber to confirm what the St. Louis plumbing code requires for the drain connection before you buy parts.
Think about service access
A filter change or a membrane swap should not require emptying the whole cabinet. Leave a clear path to the shutoff valve and the filter housings. Keep the tank where you can slide it out without moving the disposal or the trap. If children or pets like to open the cabinet, consider a latch that keeps tubing and loose parts out of reach.
Keep the faucet hole in mind
The faucet hole matters too. A separate reverse osmosis faucet often needs its own hole in the sink deck or in a countertop. Check whether the deck is solid, whether there is a pull-out sprayer taking up space, and whether the existing holes are large enough for a new fitting. Some older sinks have thin decks that will need a cover plate or a new faucet altogether.
A simple checklist before you decide
- Empty the cabinet and photograph the layout.
- Check the cold supply valve, the drain trap, and any disposal.
- Press the cabinet floor and the wall backing for soft or damaged wood.
- Measure the usable depth, width, and height, including the door swing.
- Confirm a faucet hole or deck space for the reverse osmosis faucet.
- Write down the local code requirements for the drain and air gap.
- Leave room to reach filters and the tank without taking apart the sink.
When to call a professional
If the supply valve leaks, the cabinet floor is soft, or the drain connection is unclear, stop and get help from a licensed plumber in the St. Louis area. Taking a little time to check now can prevent water damage later. Bring your photos and measurements to the appointment so the conversation starts from facts instead of guesses.