actually, they will hold water. the silicone they use is the same silicone they use on aquatic tanks. the difference is in the thickness of the glass. that's also the reason that those are cheaper than the aquatic version (except for the $1/gal sale). they put the label on it so people don't get this one because it's cheaper and then have their house fill up with 40g of water. but they will not hold a lot of water, no more than half way, which is more than you probably planned anyway