How much water should you carry on the Highline Trail from the Logan Pass trailhead?

Carry at least 2 liters per person, and more on a hot day, because there are no reliable water sources between Logan Pass and The Loop. That is unusual for Glacier and it catches people out: 11.8 miles of exposed, high-line walking with about 800 feet of gain and then a 3,000-foot descent, all without a refill. The one exception is Granite Park Chalet at mile 7.6, which sells supplies seasonally but has no running water, so do not build your plan around it.

The descent is the other half of the water math. The drop from Granite Park to The Loop loses 3,000 feet in 4 miles of switchbacks, usually in afternoon sun. Trekking poles and a reserve half-liter make that stretch far more pleasant.

On logistics: the hike is point-to-point, so most people park at Logan Pass (arrive before 7:30 to 8am or ride the shuttle up) and take the free park shuttle from The Loop back to Logan Pass at the end. The Loop's own lot holds only around 20 cars, so counting on parking there is a mistake.

If you add the Grinnell Glacier Overlook spur, budget for it: 0.8 miles and 1,000 feet of gain each way, with no water there either.