Once brewed the filter coffee is good for around 2 days.
However once you brew the coffee it's at it's best quality in the coffee maker for around 1 hour and after 1 hour the coffee starts to get stronger and stronger when the coffee machine is left on and heating the coffee.
When brewing coffee it's best to drink the brewed coffee within 1 to 2 hours of brewing it or it loses it's flavor and quality.
The coffee will remain safe to drink after a day but it won't be as tasty.
I will sometimes brew coffee and not finish the whole pot.
When I have leftover coffee I will allow it to cool down and place it in a jug and then refrigerate it.
The next morning or day I take the coffee out and pour it into a cup and reheat it in the microwave after diluting it with a bit of water.
It's not as tasty as fresh brewed coffee but it still is good.
I also sometimes add some of the cold day old coffee to ice cream which makes the ice cream taste great.
When brewed coffee has gone bad it will start to mold and if the coffee has mold in it then it should be thrown out.
I have also left a half pot of brewed coffee out overnight and then reheated it the next day and consumed it without any health issues.
As long as the brewed coffee does not have any mold then it is okay to drink.