I have spent several weekends car camping and have spent 2 whole summers in the woods at a boyscout camp. I have recently been looking into backpacking. I have found a local state forest that has a 15 mile looped trail and I think it would be a great opportunity to give it a go, they even have 12 backcounty sites.

My question is this: is there any way to estimate how much water to carry? There arent any readily available places on the trail to fill up (no taps, ponds, springs, streams, etc)

Its about a 15 mile hike, I would do it in 2 days (spend 1 night). I need enough water for drinking, cooking, and washing for the 2 days. I also want to try and pick a weekend that has mild temps (60 - 80 degrees)

Dont want too much due to weight, but also dont want too little for obvious reasons