I think I would take water. I had a portable without water for 6
months while we did modernization (what a joke) and it was do-able,
but not fun. I had 5 gal. buckets half filled, to fill water cups,
another for dirty water, and collected brushes at the end of the
period and washed them myself on my breaks. It was no fun.
I'd love to trade my classes of 30 -35 middle schoolers for yours of
15, but that is another problem altogether.