The cloudy water left after you boil potatoes can contain some of the starch and minerals released during boiling, so it’s fair to wonder whether you’re pouring something useful down the drain. These potato water uses range from low-concern to not recommended, and they all depend on one rule: the water must be cooked without salt. It’s the same save-the-liquid habit as rice water, but with a food safety catch you should know about first.
The short answer: the lowest-concern uses are watering plants and giving a pot a quick pre-soak, and both require water from potatoes boiled without salt, cooled completely. Using the water in soup or bread is a common kitchen habit, but Germany’s federal risk assessment institute advises against reusing potato cooking water for food at all. Salted water is for the drain.
It has to be unsalted. Salt in potato water is hard on plants, because salts build up in the soil and make it harder for roots to take up water. It also makes soup and bread dough easy to oversalt. If you season your potato water, pour it down the sink.
Two lower-concern potato water uses
1Water your plants, occasionally
Verdict: fine if it was unsalted and has fully cooled, but don’t expect a fertilizer. USDA’s Agricultural Research Service found that cubing potatoes before boiling reduced their mineral content by as much as 75 percent, which shows minerals are lost during boiling, and some of them end up in the water. We found no study showing that potato water gives houseplants a meaningful dose of nutrients. Our reading is that it’s unlikely to, so think of it as a reuse of water, not a plant food.
Salt is the real problem. Texas A&M AgriLife Extension’s soil salinity guide explains that plants struggle to draw water from salty soil, and Oregon State Extension lists brown leaf tips, wilting, dropped lower leaves and stunted growth as signs of salt buildup in houseplants. Let the water cool completely, use it promptly rather than storing it for days, use it only occasionally, and as a practical precaution don’t let it sit in the drip tray. If a plant gets salty water by mistake, the University of Maryland Extension suggests leaching with at least three times the pot’s volume of fresh water.
2Pre-soak a pot
Verdict: reasonable as a pre-soak, but not proven to clean better than warm water. If a pot is going into the sink anyway, a bit of cooled or warm unsalted potato water can loosen leftover food before you wash it. We found no research showing it cleans better than plain warm water, so treat this as a second use for the water, not a cleaning hack.
Two food uses the BfR advises against
Why these two come last. Germany’s Federal Institute for Risk Assessment (BfR) says consumers should not reuse the water in which potatoes have been boiled, because some of the glycoalkaloids (natural toxins in potatoes) can pass into it. Poison Control notes that cooking does not eliminate glycoalkaloids from green or sprouted pot
