I leave my children free access to their cups and water via the filtered water dispenser from the refrigerator. I prefer if they reuse their cup throughout the day, but if they don't, putting it in the dishwasher is preferred.
I walk around and pick up all through the day (You know.. so it doesn't become a massive disaster) and some days each child will have multiple cups that they have set in random parts of the kitchen and school room, with small amounts of water left in them. With 5 of them doing this (the little guy isn't quite there yet), I'm sure you can imagine how many cups I'm walking around picking up. Today was one of those days and all I could think of was "Am I in the movie "Signs"?" I'm just waiting for an Alien to come busting through the door any minute now.
Hmmm, where's my baseball bat?