pH BULL****!

Ok so i got a new digital pH tester. the Oakton ph1 i believe. So my first time using it i put it in some calibration solution to check its accuracy and it was off so i calibrated it. Now i got to feed my girls and I have some bottled water and checked the pH it said 8, thinking that was a bit high i checked my tap water and it said 7.4. i then checked some of the water you go to save mart and fill your 5 gal. buckets with and that read like a 6.4.
Now is it typical for waters to range in pH like this or is my little pH tester freaking out?
And which water should i use out of the three i talked about?

Thank you for your help :]

is normal, we can't tell you what pH you want. cause you didn't say how you grow. for example my hydro likes me to range from 5.6 to 5.9. where fox farm recommends pH between 6.3 and 6.8 with their ocean forest soil. soo...

P.S. check your pH after you add yer nutes cause they change the waters pH generally

Yes it is very normal. Use the 6.4 ro water. That is correct for soil and you don't have to drop it much for hydro. Just don't assume it will be the same every time.

PH can change daily in a hydro system. I calibrate often. Especially because I have a cheap meter.

my bottle water is 8.0 aswell and tap is 7.6, always check after nutes!