Check my short trip report from the range last weekend.
Here's how we handle water on the range:
We start at Roostercomb with minimal water (less than 1 liter per person). That takes us over Roostercomb and Hedgehog in the cool of the early AM.
In the Hedgehog / LWJ col is the junction with the W.A. White trail. A couple hundred feet past that junction on the way up LWJ, the headwaaters of Deer Brook flow right next to the trail on the right. That's pretty reliable most years, and had plenty of water last weekend. We filter 2 liters per person there. That carries us over the jaws, Armstrong, Gothics, Saddleback and Basin.
As was pointed out earlier on this thread, Haystack Brook in the Haystack Basin col is reliable. We filter about a liter and a half there. That carries us over the Haystack shoulder and Marcy.
On the way down Marcy to Slant Rock, John's Brook has water shortly below the trail junction, although we usually have enough to walk out to JBL and use the handy outdoor faucet.
Other water on the range requires a trip off the ridge and off the route. If you run into water trouble, you can usually find some about 10 minutes down the wolfjaws notch trail and about 5 minutes down the orebed trail.