You can try adding baking ...
Published by Chetan Shukla, Clean Environmental Technologies Pvt. Ltd. - Director
You can try adding baking soda to the water. Getting the water to a pH of 9 is possible but you must consider the taste of the water.
After treating water with RO you loose trace minerals from the water. It is very essential to introduce these back into the water and can be done by passing the water through a remineralizer.
Many companies in the U.S. sell remineralizing cartridges.