How do I determine if I need to dry camp?

Any tips for how to determine ahead of time if I need to bring enough water to dry camp?

I'm going camping in Butano State Park (California), there should be a small creek near camp (Little Butano Creek), however the only water gauge I can find is past a fork downstream (4 Cu. ft./s). Is there another way I can guesstimate if there is enough water flow to be safe for filtering?