I have a houseplant in a pot with drainage that I put into another pot without drainage. I should have gotten a larger outside pot because the smaller plant pot ended up being too tight a fit at the top. A while after watering I realized that the water wasn't going to evaporate and would be stagnant. Can this water be dangerous (as in anaerobic stuff going on)? I don't want to leave this outside because an animal could drink it so I have been leaving it and put chopsticks between both pots to try get some air to it but it still didn't evaporate. Any ideas on disposing of this water safely? Thanks!
Follow the advice given in the other answer (separate the pots, empty out the water) maybe taking it outside first and wearing rubber gloves if you don't want physical contact with the dirty water. Find another tray or outer pot to stand the plant in, and after you've watered, always empty the outer tray or pot after 30 minutes.
When you ask whether the standing water can be dangerous, its not clear whether you mean to life in general or your plant in particular - certainly, it is not healthy for your plant to be standing in contact with that all the time, and yes, anaerobic activity will be going on and the balance in the potting medium will change and become 'sour' and may eventually kill the plant. Whether its dangerous for human beings is another matter - I suppose mosquito larvae might breed in it if it could get in there, and it will not contribute a pleasant fragrance to the air, it will become very unpleasant to smell because the of the type of bacteria it will encourage. I certainly don't think you should wait for it to 'evaporate', specially not indoors, it needs to be dealt with as soon as possible, particularly if its a warm or tropical climate where you are.