I have tested my water for pH. My API test kit tells me I have high 7's, the little meter I got for soil pH tells me a little under 7, and my paper strip tells me 5.3.
My gut tells me that the chemistry of the API test kit would probably be most accurate.
But, goodness gracious, what is a guy to believe? After all, the difference between 5.3 and 7.8 is somewhere between 100x and a 1000x variation.