Ok. Think outside the box a bit.
You can tame any animal very easily REGARDLESS of whether or not water is available.
I'll share my taming trick:
The orange blocks represent fence sign posts. The purple block represents a dead mouflon/auroch/boar that you just killed. The blue blocks represent your positioning. Preparation:
Fence in the mouflon/auroch to separate the 2 you will be taming. You should tame 2 because it will take about the same amount of time to tame 2 as it does 1. The other will be ready and probably agro you moments after quelling the first if not while you are trying to get the quell off.
Fence in 2 other mouflon/auroch separately (so you can kill them and move their corpse around without getting attacked by the others.
Before you begin you should have 4 mouflon/auroch alone in their own fenced in areas. It doesn't have to be the same dimensions as the picture above, any dimensions will work using this technique.
Kill off the first 2 mouflon/aurochs. When they are dead, jump in a boat or walk far enough away so that you de-aggro the rest of the herd. This is important since you will be opening up a section of the fence for the remaining 2 to be tamed.
Go back and open a section of the fence signs. Lay one of the dead corpses in front of it as to cover the opening. This needs to be carefully placed such that you can get in and out of the area, but not big enough for the auroch/mouflon to get out. You can test it by agro'ing the animal and run away in a boat if it does get out. You will know if it is set correctly, because it will be tough for you to get in and out, however, it will be possible.
Call down the thunder till you get about 36ish IP. You can do it with a lot less, but you'll probably mess up the first few times (getting stuck). Run in close and sidestep, run out. Since you can get in the fenced area, you will be able to hit the animal but it cannot get out. IF you stand there and don't move away, it can hit you.. so don't stay right next to it. Repeat until you have max combat advantage. Then, move in and consume the flames. Lastly, quell the beast (can do from a distance).
The next animal will be ready. Go do the same to that one. If you take too long, keep in mind that the corpse can decay. So don't take like 2 hours to do it. It should take about 30-45 mins to tame the 2 depending on how good you get at it. Note that aggro/attacking the other animal in the herd generally causes the other to re-aggro you faster than normal. So, it can be faster to tame 2 at the same time than just 1 by itself. Note that you'll also need 2 ropes equipped. Don't leave the area, don't un-equip the ropes and don't let any friends attack any of them or you will bug your animal and it won't re-aggro you.
You need to quell 5 times to tame each animal fully.
This same trick can be done using the boulders from a cellar to tame a boar easily since boars can't break them.
Also, you can use a modification of this trick to get an animal "stuck". This requires building the entire roundpole fence with a gate. When the animal is halfway between the gate, you close it. This causes the animal to get stuck and you can walk in/out as you please to attack it. I generally don't use this method because it's faster to just lay signs than it is to gather the wood to build the whole fence. Also, my marksmanship is high enough that I can kill the blocking animals faster than it takes to build the whole fence.
If you can't kill mouflon/auroch yet with MM, then you should use the gate trick.