Of course RO is not the only way to go.
Good thing about RO is that about 99.5% of dissolved solids are removed from the water. Since tap water from city lines generally are treated, it prevents continually adding any dissolved solids into your tank that stay there because evaportation only removes pure water from your tank.
Along with RO, you may want a Deionization filter, or what ever its called, its the DI part. this will help remove phosphates, silicates, and nitrates from the water.
