I think that collecting the rain water is what I would have done. Even if I thought I was only a few miles from a water source I would still fill up with the rainwater. After all rainwater is always sanitary and and tastes good.

I realize you didn't know that you would have to abort the trip. But I still would have done it because I'm paranoid about having enough water. In fact (true confessions time here) I'm not a true ultralighter because I carry too much water. I start getting nervous when I have only 2 liters in my pack. I read these stories about ultralight backpackers who drink up in the morning so they don't have to carry much water until the next source. Not me. I don't have enough faith that the next source will work. Silly perhaps but that's me.