you should talk to the property owner. 99% of the time theyre ok with it and 300 gal/mo is nothing. 3000 gal/mo is barely anything.

i have an identical (opposite) setup with the family who lives downhill from me.

the concern is usually that you can get squatters rights to the water if you're taking it for long enough. and while you might be cool, what if you sell to someone who isn't.

so its best to keep this sort of stuff out in the open.