If you ask at the desk in the Panther Junction Visitor Center (VC) they will give you a 8x10 map of the trail drawn on a topo base that has a mileages and features marked on it.
I recommend a route that goes down the North Fork, over to the big sandbar below the South Fork junction, then up the South Fork to the "splitrock" campsite along the rim (assuming you want to do this as an overnighter and not a day hike). You could do it as a day hike but it's a long dayhike and there was a fatality on this trail a few years ago when a couple guys did it as a dayhike and one of the guys (in his 30's as I recall) couldn't make it back out and died of dehydration/heatstroke. He got within 1 mile of the parking lot and his buddy went for help, it got dark and they found him dead the next morning.
I have filtered and drank water from the Rio Grande with no ill effects, it was cold, relatively clear, and a bit limey tasting but actually much cleaner than most springs in the park with little algae. There are also some unreliable tinajas in the lower canyon of the North Fork but these only hold water for weeks (not months) after rains so don't count on them.
There are good campsites along the river near both the North and South Fork Junctions and this is a very isolated and scenic area. You don't have to worry much about cross-boarder traffic along the river in this area (it's too isolated) but don't leave any valuables in your vehicle at the trailhead.... TWWG