Brake Fluid Question -testing for water

Not sure about your product: water is more dense than BF, so it accumulates in the lower part of the system. Unless you collect a sample in the caliper you will probably not get a proper overview of the real condition.

I change the fluid every year. ATE typ200 fluid is cheap and a stellar performer when fresh. Once paired with speed bleeders, that's an half an hour /one man process.

High performance fluid do not last long. If you want to enjoy longer interval, go for lower performance products. In the long run they perform better.

 

I have used one of the testers for years. A blessing and curse of DOT 3,4 +5.1 brake fluid is it becomes a solution and very well mixed. So testing anywhere it will read about the same.

The curse of DOT 5 is it will will not go into solution so as you point out it sinks to the bottom where the heat is concentrated and boil at 212 F. Very poor choice of fluid and it is widely believed if it was not a powerful corporation like Dupont it would never have been approved. The Germans didn't. It failed TUV tests.

To the OP. You will be lucky if it regularly takes 2 or more years to get to 2%. I used to be in California and now in Texas. I seldom saw that little water content in California. In Texas over 3% in one year is quite common.

 

What rifeldriver said it will vary a lot regionally. In the Northwest were we don't really have the humidity issues that Texas and Florida has we see 1% per year.
Its still the easiest insurance to change it annually.

 

OP: I have used the exact same tool for some time now..its inexpensive and quite effective..
Brake fluid goes through heat cycles which varies according to use...just like any other fluids this takes its toll on its ability to perform which is why there is service intervals.
Brake fluid is very hygroscopic which makes perfect sense considering its use....as others have indicated this percentage reading has the potential to accelerate in climates with higher humidity levels.
Back to the tool: I would not worry too much if you get 2% if the tool sometimes shows a occasional 3% I would consider a brake fluid flush.

Just as a FYI: My old neighbor had a mid 2000 Chevy 1/2 ton one day while chatting with him we were taking a peak under the hood and I noticed very dark brake fluid so I tested it with this tool and it pegged the led's 4%>...this was a truck that lived in So.Cal its entire life but did allot of trailer towing which goes back to my previous point of increased heat cycles affecting the brake fluid quality.
Hope this helped.