Linda's question prompted a test of MilQ water from our Millipore
water purifier, extremely clean, and very carefully monitored.

pH of 6.4 (one large container) and pH of 6.7 on a newly collected
container.  John Kiernan's statement about water sitting in a full jug
vs a partially filled container was well taken.  We used to use RO water,
until the green algae bloom created havoc in too large a tank and not
enough thorough cleaning, MilQ system was installed PDQ!

This water is used in a histo setting for everything, waterbaths, buffers,
rinses, etc.  and by molecular biologists doing cell cultures, monoclonal
antibody production, Western, Northerns, transfections, and all the black
magic they do.

I know that making up Sigmas Dulbeccos PBS in this MilQ water (100 g/liter)
results in a pH of 7.4, without further adjustment for immunostaining, a
lovely plus for my lab.

Gayle Callis