The internal Ph is controlled by the body , not by what we eat or drink, I'm talking about the blood, lymph etc.
The Ph of the skin, gut, vagina etc should be acidic, and we can manipulate these areas with what we eat, and what we use topically, but when people do this and these areas become alkaline, thats when the trouble starts. Trying to manipulate the Ph of the body is what puts stress on the buffering system.
The Ph of the stomach should be very acidic, it is also possible to manipulate how much stomach acid we have, but why would you want to decrease the stomach acid with alkaline drinks etc. This is where most problems with candida, gut flora, undigested food, etc , come from.
Eating a well balanced diet of good organic foods, is a great idea for everybody, what I disagree with is wrapping that idea up with a load of hogwash about alkalising the body blah blah blah.
Instead of worrying about what your ph is, eat a good diet, get regular exercise, lessen the stress in your life, don't use drugs that will kill your gut flora, supplement what you don't get in your diet, (eg: minerals, if you live in an area with poor soil), if you do these things, you will not have to think about Ph, as your body will be happily taking care of this, and you will not have candida overgrowth.
Like my Dad always said, "If its not broken, don't fix it"