I think the parents are being a bit nit-picky, questioning you so much, but I do the same as the above. Cheap sippy cups with cold water outside, but mine have to stay on the step by the door. They can go over and take a drink as often as they want, but they're not to be running around holding it. It eliminates my needing to take them all inside or send my 6 year-old in for water, but still at least stops a lot of the mess.