Hi!
I bought a used bike with Promax for hydraulic brakes. I got it cheap because both brakes were non-functional, the previous owner said he didn't know about hydraulic brakes. These (Promax) do with mineral oil, not DOT fluid. I, however, have never done bicycle brakes in my life, and it felt like a challenge. Knowing that I would probably spill lots of oil which would be smeary, and still probably not getting it right at the first attempt, I decided to "play around" with tap water in the syringes, like a rehearsal, before going sharp. Here, you probably shake your heads and mumble "Oh, you foolish boy!", but anyways, I did. So, I actually got it right sooner than expected. I tried the brakes and they are really crisp, brakes work perfectly. Now, I'm aware that water is not to be used for (at least) three reasons, being 1) it boils, 2) it freezes, 3) it corrodes.
Now, let's say I live in a tropical place, they will never freeze. This leaves the corrosion and boiling. Say I never use hard-on force and bicycle in snail speed so I just need to gently touch the brakes to get to a halt, in short or in whichever case, the boiling will not occur. This leaves me with the corrosion. My question is, can you estimate how long it will take for the water to corrode and destroy the calipers? Are we talking a week, a month, or a year? Hard to give a theoretical answer I guess, but I find it better to ask you guys for guesswork rather than asking ChatGPT. I _will_ get to putting the real mineral oil in the system, eventually.
Everyone else…including you…have already told you how dumb you are. Yea, it’s dumb but… Water is an incompressible liquid. Although others think that there are materials in there that can be damaged by water, I don’t believe that there are. Rubber seals will be unaffected. Metal parts in the levers and calipers are made of metals that aren’t really water reactive. The pistons are probably heat insulating phenolic materials to keep heat from being transferred from during braking. While you probably should do something about this sooner than later, it’s not like you’ve ruined an expensive part. Just replace the brakes (did you do both front and rear?). Replacement brakes can be found for between $40 and $70 that are either Promax or Shimano (better choice).