Follow these steps to always have bottled seltzer water.
1. Get a pressure safe bottle (I am reusing one that held seltzer previously) and clean it before use
2. Fill it up with water leaving about 1-2 inches of head space
3. Get the water cold by refrigerating it as cool liquid will better dissolve gasses and in this case carbon dioxide.
4. Replace the normal cap with this carbonation cap and screw it tightly
5. Force carbonate the bottle by applying 30 PSI of carbon dioxide and shake it or ro
