Whilst looking for something else that Wurth make, I came across this gadget on a web site. It's got two metal prongs poking out the bottom of it. You dip those prongs into brake fluid, press a little button and it tells you how much water is in the brake fluid. This is VERY useful. Water and brake fluid are a bad combination. Moisture in brake fluid makes it crap... brakes don't work properly and it's time to flush and replace the fluid. I actually do this with my taxi every three to six months