Is it right to assume it's municipal water you're using? Some municipal systems draw water from multiple sources, and it's possible yours does the same. I'm also assuming you're treating for chlorine with Campden tablets.
RO water is your savior when it comes to brewing.
Yep, campden tablets used forever.
I've got another 4 kegs that I just tested this week. They all have the soap to varying levels. I brewed all of these on the same day.