Storms in St. Louis can knock out power for hours or days, and sometimes a water advisory follows. If you have an under-sink reverse osmosis system, it helps to know ahead of time what keeps working, what stops, and what to check once service returns. Most standard under-sink RO systems run on household water pressure alone, so a power outage does not stop them by itself. The details depend on what your particular system includes, so start by looking under the sink.
Find Out What Runs on Electricity
Open the cabinet and identify each part of the system. Many under-sink units have only filter housings, a membrane housing, a storage tank, a drain line, and a dedicated faucet. None of those need power. If your setup includes a booster pump, an electric permeate pump, or an automatic flush controller, those parts will stop during an outage. Write that down on a card and tape it inside the cabinet door so anyone in the house can read it.
Also confirm whether your storage tank is full before a storm arrives. An RO system fills its tank slowly, and that stored water is what you draw from during a power loss if the unit cannot make new water. A full tank is the simplest backup you already own.
Know Where the Shutoff Valves Are
During an advisory, you may need to close the cold feed to the RO system so no untreated or uncertain water enters the filters. Find the small valve on the cold water line that feeds the system, and test whether it turns smoothly. Stiff valves are common in older St. Louis homes, and a valve that has not been moved in years can seize. Turning it once or twice on a calm day tells you whether it will work when you need it.
Also locate the main shutoff for the whole house. Know which direction closes it, and keep any tool needed to operate it in an easy spot. If you are unsure whether your valve will hold, have a licensed plumber look at it before you need it in an emergency.
Plan Your Drinking Water Supply
Keep a supply of bottled or otherwise stored drinking water on hand for emergencies. Local authorities, including your water provider and county or city public health offices, issue guidance during advisories. Follow their instructions on whether to drink tap water, boil it, or avoid it, and treat that guidance as the rule even if your RO system is running. An RO system reduces many substances, but it is not a substitute for official direction during a declared advisory.
Keep a few clean containers ready for storing water and label them with the date. Replace stored water according to the container maker's directions.
Restart Checks After Power Returns
When the electricity comes back, do not assume the system is ready to drink from right away. Run these checks first:
- Look under the sink for drips, wet spots, or loose fittings, especially where a pump or flush controller was disconnected.
- Confirm the cold feed valve is open and the storage tank is refilling.
- Let the faucet run for a while before filling a glass, so stagnant water in the lines clears out.
- If a pump was off, check that it restarts on its own or follow the manufacturer's reset steps.
- Check the drain line for any kinks or disconnected sections.
If you saw a water advisory, do not start drinking from the RO faucet until local authorities say the supply is safe again. Once it is, flush the system and discard the first batch of water as your unit's instructions describe.
Sediment and Pressure Changes
When water service stops and restarts, pressure in the lines can change sharply. That change can stir up sediment that has settled in a sediment prefilter or in the supply pipes. If the water looks cloudy or carries particles after a restart, run the cold tap for a while and let the water clear. Then check whether the prefilter needs replacing. A worn sediment filter cannot do its job well, and it is worth knowing its age and condition before the next storm.
Keep a Simple Outage Note
Write a short note that lists the location of your shutoff valves, the parts that need power, the date you last changed each filter, and the phone number of your water provider. Keep a copy with your emergency supplies. Review it once a year, ideally before storm season, so the information is current when you need it.
A little planning now makes a St. Louis outage far easier to manage. Know which parts of your RO system depend on electricity, keep stored water and a full tank, test your valves, and follow local guidance before drinking from any tap.