A couple of my personal favorites (with water) : the Tanglewood trail at the very end of CR 43 (left at the Y) in Bailey (nice one for tourists) or he could try the Maxwell Falls trail above Brook Forest. Try not to do them on the weekends.
i don't know if reynolds ranch open space on foxton road has water this time of year. i know when we walk it in the spring there is a small stream.
we also walk the platte river road near foxton on weekdays and enjoy the north fork of the south platte which is running higher this year.
bumper sticker - honk if you will pay my mortgage
"The problem with Socialism is that eventually you run out of other people's money." attributed to Margaret Thatcher
"A wise and frugal government, which shall leave men free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned - this is the sum of good government." Thomas Jefferson
Brookside McCurdy in Bailey was the first trail I found when I moved up here 15 years ago and I still love it. It does not have water all the way but there are several little creeks that are still running (very unusual). All the other one's mentioned are very nice too. Tanglewood is mostly in the shade/trees, something to consider in the fall.
Buffalo Creek road is good too. Mixture of sun and shade. The road follows the creek. Not very technical, but a nice trail to take dogs out on. Just be sure to respect the private property at the beginning of the road.