ive heard you can put water in your brake instead of oil?
is this true or just works in some brakes…
water evaporates and turns to gas… it seems like you would constantly have to bleed the line, but I’ve never tried it.
I’ve used water in my Magura brakes for a couple years now. No problem with it. If you have a big tub, you just fill it with water, throw the whole brake (lever, line, and slave cylinders) in with the bleeders off, and pump the lever until no more bubbles come out. Keep 'em underwater and screw the bleeders back in. I’ve never regretted changing over.
The issue bikers say can come up is with heat–that too much braking for too long can generate heat that boils the water, with a result like having air in the lines. A bike going on a long downhill might be able to generate that kind of heat, but on a unicycle it seems unlikely. Definitely not an issue with the kind of riding I do.
I also ride water in my Magura since I broke the cross over the first time. I didn’t want to pay to get it bleeded again so I used water. It works fine, I didn’t had any problems. It’s also really easy to bleed and probably easier than bleeding with mineral oil. You just can’t use your magura under 0 degrees if you bleed it with water 
I’d think water ought to work a lot better in the Magura rim brakes unis are using (almost nobody on 2 wheelers uses them any more) than a disc brake. The heat transfer to the fluid is a lot less with all that brake pad in between. I’d definitely not recommend water for use in a disc brake.
What about using the unicycle when it’s freezing, even if you don’t use your brake? Does the frozen water harm tubes or brake? As water expands when freezing, I would guess at least the tubes will burst.
I use water in my maggies. It feels nicer than the proper oil and is far easier to bleed, I bath bleed them.
Some people say that it corrodes the inside of the cylinders and the lever, but you need oxygen and water to corrode aluminium and if you’ve bled it properly there shouldn’t be any air in there 
One issue me and a few of my trials biking friends have had is with the pistons swelling up and jamming in the levers. This is the only issue that I have ever had with a water bleed, and one that Adam at Tartybikes explains in this thread: http://www.trials-forum.co.uk/topic/163793-using-water-and-got-sticky-pistons/page__hl__sticky+pistons
You can mix some antifreeze in with the water so you can use your brake in cold weather.
For freezing and corrosion worries use antifreeze formulated for aluminum engines, this should not damage the seals.
There is a boat steering manufacturer who uses this in there systems and they work extremely well!!!
Just as a thought what do the manufacturers of the brakes say? does it void any garentee’s ? Just some of the questions going through my head, and if you do use antifreeze please don’t leave it laying around in a bowl as cats love it but it is poisoness and will kill them ! 
I used water in my first set of Magura brakes for over a year. (Probably would still be using them if I hadn’t destroyed them during an extremely muddy 12 hour off road race a couple years ago). The only issue I ever had was riding in cold, i.e. near or below freezing temperatures.
One cold afternoon in the winter (in Alabama we don’t have to worry about too many days below freezing) I was out riding, totally oblivious of the fact that I had water in my brake lines. It wasn’t quite freezing out but it was very windy. Anyhow I’m riding along and all of a sudden my wheel locks up and I go tumbling. My brake line had frozen and forced the brake pads to lock up against my rim! Ha! Luckily I wasn’t too far from the end of my ride so I carried my uni out to the trailhead.
I’m running my newer set of Maguras with the Magura “blood” (thanks Brycer) and haven’t had any issues. If I ever have to bleed them again I’ll probably go with water or something similar as the tub bleed method was so much easier (I don’t have the right bleed equipment and am a clutz!).
so when i do this shall i take the brake pads off or leave them on?