Reverse osmosis is basically a filtration system. With the proper filter less than (1 micron) it is effective at removing nitrate and microbiological contaminates. However, it requires a great deal of pressure and generally processes water slowly.
Like distillation, it requires energy to run. It is also a rather expensive alternative. It is however, the most effective overall treatment system. Reverse osmosis can remove nitrates, micro biologicals and lead. It is partially effective on organic chemicals and chlorine and can improve odor as well.