Water Filtration is a key component to having and maintaining a healthy aquarium.  Reverse Osmosis or known mostly as RO/DI systems are the best option for purifying your water for aquarium use.  Making sure your TDS (total disolved solids) are zero when coming out of your Reverse osmosis system is essential in maintaining a healthy aquarium.  

Fragtastic Reef sells and recommends RO/DI systems with TDS monitors, high quality sediment and carbon blocks, and high grade DI resin.