Standing water in Nespresso canisters loses protective chlorine within about 24 hours, removing its antibacterial defense. Without chlorine, canisters become conducive to bacterial growth and can reactivate dormant organisms like Legionella, especially above 68°F, increasing the risk of gastrointestinal illness. Water sitting out absorbs CO₂ and becomes more acidic, negatively affecting coffee flavor and pH balance. Daily water replacement is recommended to maintain safety and taste quality. While an overnight glass might not be immediately harmful, prolonged storage degrades water quality and heightens contamination risk, making routine refills the safer choice.
Tap water is protected by chlorine, a chemical artificially added to kill bacteria. Yet, chlorine can evaporate in as little as 24 hours. Because of this, a Nespresso canister quickly becomes growth-friendly for new colonies of bacteria, and creates a favorable environment for dormant ones, such as Legionella, to reactivate - especially at temperatures over 68 degrees Fahrenheit. The longer that water sits, the higher that risk becomes.
There are plenty of false facts you shouldn't believe about your Nespresso; don't be fooled by the myth that leaving water in the canister is okay. It's worth noting the quality deterioration, too. The reason water tastes differently after sitting out for a long time is the absorption of CO₂. Leaving Nespresso tanks half-full is a one-way ticket to an acidity spike, and the last thing consumers want when balancing the delicate pH of coffee is off-tasting water.
Daily changes seem to be the sweet spot. Will a half-empty tank that's been sitting for over 24 hours do harm? It's a similar question to whether it's safe to drink that glass of water you left out overnight; technically, no, it won't hurt you, but it's not worth the quality deterioration or risk. There are quibbles over hard vs soft water, and which to use to brew coffee; swapping acidic-tasting remnants
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