I'm not sure if I count this as a close call, but last May my wife and I were on vacation in Grand Staircase and decided to take a day and do the Red Breaks Big West Fork Slot. Planned it in great detail and decided that after we were done with that, we were going to scoot on over to the Cosmic Ashtray and then back down to Harris Wash. With a nice sunny warm May day, we headed to Harris Wash early and then up Red Breaks wash to the slots. Worked our way through the slot and over all of the obstacles. Tough, but fun hike. As we headed out of the narrows and worked our way towards the Ashtray around noon, we found the geography of the land made it difficult to just hop over that way. No big deal, we worked our way over ridges and realized that we had to work our way further north as eventually the ridges would smooth over and eventually be able to be crossed. We ended up doing this around 1 in the afternoon and the day started getting very hot. As I realized that I had to go north through a sandy wash to eventually go east, and then eventually south about 4 miles back to the car, I thought that we were fine as long as we had water in our 3 Liter Osprey bladders. It was literally around this time when my wife said that she was out of water. After verifying that she indeed was out of water and saying a few F bombs to myself, we found a small shade tree to regather our thoughts and plans. While I knew exactly where we were and where I had to go, I wasn't able to get there due to geography and ridges I couldn't cross. I even had the Backcountry Navigator app to make sure I knew where I was. We left the tree and headed up the sandy wash but thankfully soon found slickrock. Once that happened, the ridges smoothed over and we were able to take a straight line over to the Ashtray. Meanwhile, I had to ration my 2L of water for the two of us and hoped that it would last long enough. We stopped by the ashtray for a quick exploration (our second time) and then headed down toward the old dirt road that runs to the east of the ashtray and then down to Harris wash. After a very long, dry, and sandy hike back to the car, we arrived very tired and thirsty with just a few swallows of warm water left.
In hindsight, I need to take one more liter of water per person to adjust for situations like I encountered. We did encounter one pool of water that I could have refilled at, but I didn't realize that my wife was that low on water. I also thought that I could get over to the Ashtray much easier than we did as I think that we left Red Breaks a little earlier and should have gone a little more north before heading over. In any case, it gave me new appreciation for being thirsty in the desert and more understanding of how things can go wrong so quickly on a hot day.