I use RO water but a few friends don't and I've gotten one of them to get a sample to Ward Labs and they got this:
pH 7.7
Total Dissolved Solids (TDS) Est, ppm 305
Electrical Conductivity, mmho/cm 0.51
Cations / Anions, me/L 5.7 / 5.4
ppm
Sodium, Na 35
Potassium, K 3...