To get water easily to your fortress, dig a tunnel underground, in the first layer, from the very edge of the brook or river. This tunnel should go to a place where you intend to have an enclosed outdoor area. End the tunnel there with a staircase to the surface. Next to the staircase channel a hold into the tunnel. Build a well over the channelled hole. Now you are ready except for the water. For safety's sake, you should make a stone grate and install it as a wall grate at the end of the tunnel nearest the river. Lastly, cut a channel between the river and the tunnel. Water will flow into the tunnel and your well will be functional soon afterward. An additional feature could be a floodgate controlled by a lever, to close the connection between the well and the river, but it is not necessary.
Make the well a water source zone, and then set it do the Dwarves ONLY drink from marked zones.
This is only good for non-freezing biomes, but you did not mention a problem with freezing.
I don't know if you are using the orcs that can avoid traps, but this method will work regardless. Outside the walls of your fort, make a walled enclosure with two openings. One is to the outside, and one is to your fortress via a walled hallway. Build a raising drawbridge at each opening, each controlled by a lever. One level above the enclosure, build a floor overlooking the enclosure, protected by fortifications. Post your marksdwarves there with their ammo stockpile nearby. Next time the orcs attack your fortress, leave both bridges down until a group enters the enclosure. Close the inner opening by raising that drawbridge, then close the outer opening in the same way. Now the orcs are like fish in a barrel, for your marksdwarves. Furthermore, your marksdwarves cannot rush into melee because the raised bridge prevents them from doing that. You don't need moats under the drawbridges for this to work. The raised bridges act as walls. If you want to collect the loot before dealing with the next group, just lower the inner bridge and let everyone finish doing their jobs before lowering the outer bridge.