The lower the Total Dissolved Solids (TDS) in the water, the purer it is. Our San Diego tap water has TDS of about 400 parts per million, and our Reverse Osmosis water has about 25 ppm. We tested the following brands of bottled water, and here are the TDS levels:

AquaFina "Non-Carbonated -- Purified Drinking Water": approximately 5 ppm.

Arrowhead "Mountain Spring Water": approximately 90 ppm.

Crystal Geyser "Natural Lemon Flavor, Sparkling Mineral Water": approximately 350 ppm.

Evian "Natural Spring Water": approximately 275 ppm.

Palomar "Mountain Spring Water": approximately 80 ppm.

S. Pellegrino "Sparkling Natural Mineral Water": approximately 600 ppm.

Perrier "Sparkling Mineral Water -- Low Mineral Content": approximately 250 ppm.

Sparkletts "Mountain Spring Water": approximately 140 ppm.