As a coffee drinker myself, I understand when you wake up in the morning you just want to drink it down as fast as possible to fuel your morning. Because of this, you may leave water in the coffee maker the night before so the next brew will be as fast as possible – but is okay for both me and the coffee maker?
Sure the water is safe to drink even after days of just sitting in your machine, but it will get stale. Your water being stale is nothing to ignore though, brewed coffee is 98% water so the quality of the water you use to make your coffee is important enough to negatively change the taste of it.
Water can get stale just 12 hours of being in the open because of carbon dioxide. If you want your coffee to taste its best, you should empty then fill the coffee maker with fresh water every day.
Bacteria getting inside your coffee maker can happen in a couple of different ways.
First, the bacteria in the cup/reservoir you use to add the water to your coffee machine can be transferred right into the tank of your machine. That bacteria can then grow overnight.
Then if your water is from the tap its likely to have microorganisms inside it that get transferred into your coffee maker. Though usually a small amount, it can be enough to make a difference over a 2 to 3 week period.
Depending on the hardness of your water, it can have more or fewer minerals in the water that can lead to deposits in your coffee machine.
This is even more prominent if you’re using tap water, as tap water is usually mineral-rich with calcium and magnesium.
When these deposits build up you have to descale your machine to clear all the deposits out to prevent the heating elements to be insulated resulting in your coffee being less hot and tasting differently.
It is okay to leave water in your coffee maker or Keurig overnight, but it may become stale by the next morning. The stale water will affect the taste of your coffee which is noticeable by most.
I’m the Coffee Grump. I’m a tech guy, not a sales guy. I love coffee, and I service the equipment that grinds and brews it for you. I have more than 25 years of experience in technical and customer service in coffee machinery, and I hope to share some of that experience with you with this website!