Guide · Home care
Reverse Osmosis Drinking Water
A plain, friendly guide to the small reverse osmosis faucet under many kitchen sinks: what it does, filter schedules, who takes care of it, and what to report.
Where to start
- Water under the sink?
Turn off the RO supply valve if you can reach it easily, dry the area and tell the owner. See signs to report.
- Little faucet slow, or water tastes flat?
The filters may be due. See how often filters are changed.
- Owner asked you to change the filters?
Follow the maker’s steps, and read the general shape of a filter change first.
The short version
Some kitchens have a small extra faucet beside the main one. Under the sink, it connects to a reverse osmosis system, a set of filters that makes very clean drinking water.
It is a nice thing to have in a home, and it asks for very little. The filters do need changing on a schedule, though, and the signs that they are due are easy to miss because they creep in slowly.
This guide explains what the system does, who takes care of it, and what to watch for. Please ask anytime. We would much rather hear from you early.
What the system does
A reverse osmosis system, often called an RO system, usually has several stages: a sediment filter, a carbon filter, a fine membrane that removes much of what is dissolved in the water, and a final carbon filter for taste. Clean water is stored in a small tank under the sink until you use it.
Who does what
In most rentals, filter changes and cleaning are the owner’s job. Please check the lease or ask the owner. If the owner asks you to change the filters, follow the maker’s instructions for that exact system and ask for a quick walk through the first time. These are examples.
Residents can often
- Keeping the cabinet clear enough to spot leaks
- Reporting slow flow, odd taste and leaks
- Changing filters, only when the owner asks and with the maker’s steps
Leave to the owner or a pro
- Filter changes and cleaning, in most rentals
- Sanitizing the system
- Checking the storage tank air pressure
How often filters are changed
Schedules vary by maker and by the water, but many systems follow a pattern like this:
- Sediment and carbon prefilters about every 6 to 12 months.
- The membrane every few years, or sooner if the water slows or tastes different.
- The final carbon filter about once a year.
The maker’s schedule always comes first.
The general shape of a filter change
This is the general shape, not a replacement for the maker’s steps.
- Set a shallow pan and towels under the system.
- Turn off the water supply valve to the RO system and close the valve on top of the storage tank.
- Open the RO faucet to let out the pressure until the water stops.
- Unscrew the filter housings, swap in new cartridges, and check the O rings.
- Tighten the housings by hand only, unless the maker says otherwise.
- Turn the water back on slowly and check every fitting for drips.
- Many makers say to drain and discard the first full tank or two after new filters go in.
Some makers call for cleaning the system with a sanitizing solution during filter changes. That step involves chemicals and exact amounts, so it is best left to the owner or a pro following the maker’s directions. For owners, many makers also call for checking the air pressure in the empty storage tank, often around 7 to 10 PSI.
Signs to watch for and report
Here are some common examples. This is not a complete list.
- The RO faucet trickles or takes much longer to fill a glass.
- The water tastes or smells musty, stale or different.
- Drips, damp spots or puddles under the sink.
- A drain line that gurgles or runs all the time.
If you see water under the sink, turn off the water supply valve to the RO system if you can reach it easily, dry the area and let the owner know right away.
RO system checklist
From the guide’s own checklist. Tick each one as you go. Your ticks stay on this device. These are examples; your home may need others.
All done. A fresh set of filters keeps that little faucet doing its best work.
An everyday example
A resident noticed that the small kitchen faucet had slowed to a thin stream and the water tasted a little flat. They let the owner know and sent a photo of the filters under the sink. The owner saw the sticker showed the prefilters were almost two years old. The owner changed them, checked the tank, and let the system refill. Two days later, the resident said the water tasted fresh and the faucet was back to normal.
Guides that go well with this one
How much do you remember?
4 quick questions from this guide, with a one line why for each. Totally optional, no sign in, and your answers are never saved.
Go deeper with The Perfect Plumbing
An RO system is one small part of a home’s plumbing. The Perfect Plumbing walks through the whole system, from shutoff valves to water heaters, with clear notes on who does what.
Keep this guide handy
Save this page, come back to your checklist any time, and share it with anyone in your home who could use it.
See all guidesTake it with you
- Bunklow Home Guide 111: Point-of-Use Reverse Osmosis (RO) Filter Changes and SanitizationA printable Bunklow guide to point-of-use reverse osmosis (ro) filter changes and sanitization: plain steps, how often to check, and when to call a pro.See it in the shop
- Plumbing and Water Checklist PackThe Plumbing and Water checklists in one pack, fillable on screen or printable.See it in the shop
This guide shares general educational information to help you, and is not legal advice or a substitute for a licensed professional. Bunklow does not inspect, repair or service plumbing or water systems. Rules differ from state to state and town to town, so please check your state and local rules and your lease, follow the maker’s instructions, and get local help from a qualified professional for repairs.