At the top of the water tower, you can inspect a pack to get a hunting rifle, a blanket, and 20 rounds of 30-06 rifle ammo. If you leave at this point, you won't miss any items.
If you look around afterwards, you can use the hunting rifle to shoot a distant zed, then two distant zeds. Next, you can shoot three distant walkers chasing a survivor, or sit and watch.
If you sit and watch, you can just wait and bypass a horde of zombies that come through.
If you shoot the three zombies, you can shoot the survivor, climb down to him, or watch the horde come get the survivor. Climbing down to him gives you some options to interact with him, all resulting in the options to kill him or leave him. Next, you have to fight two runners; you can use the survivor as bait for them and run, or fight. If you fight, you will have a large horde of 32 zed to contend with after you kill the two runners.
Side note: If you choose to leave him then choose to run it will bring you back to the "leave him" choice and you can go in a loop.
The survivor has no items on him.
Side note: if you just attack the horde with out going down you wouldn't die and you can get some free XP using the rifle