Hard cider is made from apple juice, and it takes roughly 10 gallons of apples to make 3 gallons of cider. Straight juice will yield roughly 5-6% ABV if left to ferment completely. So as you can see, pulped apples in water would be very watered down and weak.
A better question is what is your goal with cider? Are you looking to make hard cider, or just some sort of apple flavored drink?
I've only made cider from store bought juice (straight juice plus yeast, as well as straight juice, yeast, and sugar for extra ABV) so my experience is relatively limited. As far as I know though, you should not be using water (unless reconsituting frozen apple juice concentrate), and if you want to use fresh apples, you'll need to press them somehow.
Here's a quick link I found with a message from a well known member about a "redneck press": Making cider without a press
