I have used one of these mugs only for water and have LOVED it! I have used it for about 6 months, bought them at [...]in a double pack on a whim and they have just been the best mugs ever. They were back at [...]recently so I bought another two pack for my husband and I. This one I use for lattes and the lid pretty immediately started to stink of sour milk. I poured soap and shook vigorously, tried to scrub, sent it through the dishwasher. Still pretty nasty and getting nastier every day. I figured it couldn't last much longer at that rate so why not try boiling it. I was going to stop using it anyway, so if it got ruined it would not be the end of the world. I boiled water then dropped it in and boiled for 10-15 minutes. This is a little bit of a pain but it really does solve the stink problem... This is the only reason that I could not give this mug a 5 star rating. It's awesome!