Water test?

Ok guys, I’ve been hearing all this talk about the “water test” lately. I was wondering if anyone knows if it actually works or not? I’ve been getting all negatives so today I took a test and left it sitting and went out to trim hedges with the hubby on his day off...I completely forgot about the test which is strange bc usually I watch them like a hawk. Anyways when I remembered it I ran in and there was a super super faint line. Well I had no clue how long it took for that line to show so I assumed it was an Evap. Then I get on here and see something about the water test. ( if you have a line and put water on it then if it disappears it’s an evap and if not then it’s a true line) anyways I did it and the line is still there. Anyways I’m still thinking it may be an evap and won’t think I’m actually preg unless I get a very clear pos but curious if this actually works? Seems kinda strange to me.....