From the book, "A Handbook of Routine Urinalysis" by Sister Laurine Graff, we find the following. 

"To maintain a constant pH in the blood, the kidney must vary the pH of the urine to compensate for diet and products of metabolism." 

Your kidneys are running your body's alkaline status.

And your alkaline status is the secret they don't want you to know.

I lay it all out in the book.

Saliva vs Urine pH

TOP TEN REASONS WHY SALIVA PH IS WORTHLESS WHEN COMPARED TO URINE PH FOR ACID-BASE ANALYSIS

#10  Small Volume - small tiny volume samples don't represent the whole

#9    Difficult to Obtain - the procedure is to bring up saliva and swallow, 2x, then use the third one for the test, too hard to obtain

#8    Poor Reproducibility - when you retest your saliva sample, you will likely get a slightly different color (reading)

#7    Poor Accuracy - if you collect a second sample, it will likely give you a different reading than the first

#6    Bacterial Contamination - bacteria from your mouth will interfere with the test

#5    Food Contamination - food from your mouth will interfere with the test

#4    Spoon Contamination - the surface of the spoon that you collect it on is going to affect your small sample

#3    Viscosity - saliva is too thick and results in faded or dual colors of the test pad (or paper)

#2   Difficulty Reading - the color doesn't "lock in" so you can take a reading, it tends to change shades through a range

#1   Your Salivary Glands have ZERO to do with Acid-Base regulation.  Try Kidneys.