I think that it is more likely they'll look at us with bemused semi-contempt, much like we currently look almost all practices rendered economically irrelevant with the exception of a very few (slavery, child labor, etc).
"Man, that sure must have sucked back when they had to grow a whole darn cow just to have some beef to eat. Can you imagine how inefficient that is? Heck, the cow bits would be so valuable, you'd probably actually save the ones you didn't eat, so that you could eat them later! Imagine how absurd that would be!"
(If this dialogue strikes you as unlikely, consider what you would say to any friend who, on deciding they were done drinking from a glass of water, put a saran wrap cover on the top of the cup and put it in the fridge "so I can drink it for leftovers tomorrow". Local caching of water made plenty of sense up until quite recently, historically speaking.)
You must be from the USA?
Water costs plenty in production and produces waste due to energy requirements and chemical processing. Whilst water is cycled through their is a substantial lag involved meaning that water reserves can be damagingly depleted.
Throwing consumables away that are still directly usable is unnecessary waste - put the rest of the water on your pot plants or pour it in the kettle to use later.
One other thing, do you saran-wrap (aka cling-film) a glass of water sitting on the counter in the kitchen? Why then do that when it sits in the fridge? If you find you need a cover then use a reusable container with a cover.
Local caching of water still makes plenty of sense.