RO Units

[DiverDude]

A few things to consider:

-RO or RO/DI ?

Reverse Osmosis water is pretty much what you get from bottled water and is usually good enough. You can also drink the output of the system so that's a bonus. Adding a DeIonization (DI) stage will further remove 'impurities' (mostly salts). This is a better choice for reef setups as you have the most control over water purity. DI water isn't nice to drink though.

-Waste Ratio

Many RO units will 'waste' 2.5 Gal or more for every gallon of pure water. Of course you can collect this 'waste' and use it for whatever. Better units have booster pumps and run water through the filters at higher pressures reducing the waste considerably. A good unit will produce 1:1 good to waste ratio. All these figures will vary with the temperature of the incoming water and gets worse (more waste) when the water is colder.

-Bells & Whistles

Higher end units often include a TDS meter on the final stage. This is really handy ! You can monitor the performance of the system and know when to change filters. Some also have auto back-flush functions that are intended to keep the membrane filter clean and extend it's life. With a membrane cartridge running around $80 or so, you'd like to get as much out of it as possible.