The water was only waist to stomach height for the first 2/3rds with plentiful running in between. When the water got higher the obstacles got closer together. There was a lot of queuing for obstacles and I never got warm after that. It stopped being so much fun at that point and was more like hard work. I ran backwards and forwards between the same two obstacles at one point to try and warm up. I'd been advised by two people who'd done it before to run as fast as I could at the start to beat the queues at the obstacles towards the end of the course. I took it a bit easier as I was worried about my fitness. Shouldn't have bothered as I was fine from a cardio point of view. A lot of the people taking part aren't runners. I'm not great but can cover that kind of distance and not be too knackered.
The water temperature was only a problem because it was January. There was a very thin layer of ice on the water before everyone started jumping in and the weather forcast said it was between -1 and 3 degrees for the event day. It had been a lot colder the previous two years

Even jumping into water up to the stomach and back out again followed by runing it was still a lot of fun and no problem, just the initial shock when jumping in. No one had trouble there at all and atmosphere was superb.
If you're doing Tough Mudder in May it'll be fantastic

I've got a race that weekend otherwise I'd be up for another one. Tough guy nettle warrior for me in July instead. If you can get over to Wolverhampton it'd be a good one to do if you enjoy the Tough Mudder event.