Originally Posted by aj986s

FWIW, I think that in a cold state, water and brake fluid will probably work similarly. The problem with water is heat. Once the brake calipers get hot, the water will boil into vapor, and the vapor can be compressed, causing the softer pedal. My guess is that the problem is more likely air bubbles trapped in the system, along tubing surfaces, etc. that need to be evacuated in order to get the system completely filled with fluid. Several cycles of bleeding will usually move/consolidate these bubbles until they're finally expelled. I don't know if from a scientific/hydraulic's perspective whether liquid water and brake fluid might compress differently. And, as mentioned, water also leads to corrosion issues.

But, condensation in the Motive bottle is an issue, and getting water into the brake system is a much greater concern than for the clutch. Personally, I've resorted to only using the Motive "dry", where I monitor fluid level in the brake/clutch fluid reservoirs, and using the Motive only to generate pressure. Do need to be careful to not empty the fluid reservoir. But fewer cleanup & storage issues of the Motive.