RO water is expensive to start. RO produces waste water you must dispose of. But remember, the waste water is very like your tap water. So it can be used in applications where your tap water works well. Examples might include clothes washing, plant or lawn watering, toilet flushing.
Distillation produces clean water by evaporating the water from the input and condensing the steam.
It is highly energy-intensive, and expensive unless you have a free source of waste heat. Distillation systems tend to be low capacity. Ion-exchange systems work by exchanging cations such as calcium and magnesium for the cation on the resin, usually sodium, potassium or hydrogen. They also exchange anions like carbonate and sulfate for the anion on the resin, usually chloride or hydroxyl. These systems can be recharged and should be as the resins are very expensive.