JH: Too much water actually kills more houseplants per year than any other single cause. Monstera is no exception. As it grows, it's used to forming lots of aerial roots that cling onto tree trunks, so the roots tend to rot if they stay wet and soggy. Let the top inch or two of the potting mix dry between waterings, and if in doubt, it's better to keep it a little too dry than a little too wet.