If you use a PH meter, the reading will be sketchy with water that pure.
They don't really work at all, with distilled, or RO water, so we just call them 7.0.

Ya need Hydrogen ions to measure Potential Hydrogen, (PH).

Phenolphthalein or test strips will work.
Ours can be quite acidic depending on the vog.

Carry on.
Standing by.

Weeze