You generally drip faucets during hard freezes to help prevent pipes from freezing and bursting. The exact temperature threshold can vary a bit, but there are common guidelines.
Key temperature guideline
Most plumbing experts recommend dripping indoor faucets when the outside temperature is expected to drop to around 20°F (about -6.7°C) or lower for several hours, especially overnight or during a cold snap. Some guidance also says to start dripping if temperatures will be below 20°F for at least about three hours, or if the power goes out in freezing weather and your heating won’t protect the pipes.
Which faucets to drip
You should prioritize faucets fed by pipes that run through exterior walls, unheated basements, crawl spaces, attics, or other cold areas, because these are most likely to freeze. Many sources also suggest dripping at least one faucet on each side or “section” of the house, often choosing the one farthest from the main water line so water moves through as much pipe as possible.
How long to keep them dripping
Keep faucets dripping as long as temperatures remain at or below the freezing- risk range (around 20°F or lower), and continue until the forecast shows temps consistently above that level. If there has been freezing, maintaining the drip during the thaw helps relieve pressure so any ice can melt and move without bursting the pipe.
How much to drip
You only need a small, steady drip or slight trickle—often described as one to two drops per second—rather than a full stream, to keep water moving and reduce freezing risk. If it is extremely cold (near 0°F or below), some advice is to increase the flow slightly while still keeping it modest to limit water waste.
Hot vs. cold water
If your plumbing has separate hot and cold lines, guidance stresses letting both sides drip so neither line can freeze. For single-handle faucets, set the handle in the middle so both hot and cold water are moving through the pipes.