Second time this week I come across an article pointing out this http://m.huffpost.com/us/entry/pare...d-be-growing-mold_us_56cddfc0e4b0ec6725e4a873 I always wondered how on earth to clean that stupid valve and I've always sucked the liquid out prior to cleaning and after so it doesn't stay in because I have no idea how else to clean the stupid thing.. Safe to say I resorted to an easier to clean cup that's free flow because it was doing my nut in so much. A similar article about the sistema screwcap bottles have been going around. Though I recently bought one of them too and didn't even think about that possibility! Please be aware with these type of valves and tops as they are very tricky to clean and to check whether water is retained that can add to the cause of mold growing! Even tho both will have their story ready as to how they are properly used in the sistema story it was clear that the person finding mold in their child's screw cap used normal suitable drinks, washed and sterilised them after use! Sistema claims they're hard to take apart because of safety reasons seems like it contradicts itself a little!