How much water should you carry between Trans-Catalina Trail campgrounds?

Plan around a minimum of 3 liters of capacity per person, and treat the trail as having no natural water sources worth counting on. Unlike Sierra routes where you filter from creeks all day, the TCT is arid, exposed, and mostly shadeless, and your water comes from fixed points: the campgrounds, the Airport in the Sky at mile 15, which has refills alongside its famous grill, and the village of Two Harbors at mile 26.

The stretch that catches people is the final leg. Parsons Landing, the primitive beach camp at mile 33, has no running water at all. The system instead has you reserve a locker stocked with water and firewood, so your Parsons night depends on paperwork done before the trip, not on anything you can find on arrival.

Season changes the math substantially. Spring, roughly March through May, and fall, September through November, offer the best conditions. Summer runs extremely hot and dry on the exposed ridgelines, and the trail's 8,500 feet of cumulative climbing over 38.5 miles means you sweat out far more than the mileage suggests. In hot months, start climbs at first light, carry beyond the 3-liter floor, and take the refill at the airport seriously even if your bottles are not empty. A wide-brimmed hat and lightweight long sleeves do about as much for your water budget as an extra bottle does.