It started out as potable water but became "pure".
Potable water is the quality of the water. While most times the problem is too much stuff in the water that needs to be removed to become potable it can work the other way to where the water is to pure and needs to be reconstituted to become potable.
BeanAnimal that is a layman's definition but either way RO/DI water is not really safe for drinking and therefore not potable.
Just because some people drink it does not mean it should be drank. I could drink from my local stream but that doesn't mean it's safe or potable either.
Many of the cheap RO/DI systems reefers have will create potable water because they don't work that well. But if you have a good unit/filters/membranes/resins then you will get ultra pure water and it won't be potable.
Actually products sold in the US that meet criteria for holding "potable" water meet the criteria of the USEPA. The USEPA does not consider ultra pure water as potable. Neither does ANSI/NSF Potable Water & FDA Bottled Water Quality Standards.
While I don't want to argue the point since I know the differences an RO/DI setup isn't the ideal filtration if the intent is for drinking. Cold Sterile Filtrate system is a much better choice as it removes pesticides, volatile organic chemicals, complexed phosphates and dangerous bacteria. Most RO/DI units do not reject VOC's, low levels of heavy metals, Organic Carbons, Pesticides/Insecticides, Poly and complex Phosphates, Water Conditioning Polymers. Cold Sterile Filration doesn't remove calcium, magnesium divalent cations nor strip the water's alkaline reserve which is important to be considered potable.
http://www.epa.gov/safewater
Here's something I just found:
Ultra pure water is the perfect solvent. Presently many reef tank owners use R/O [nanofiltration], Ion-exchange resins and combinations of R/O + mixed bed resins or split bed resins + mixed bed resins producing high quality water [conductivity: 1.0µ/S-0.243µ/S] which requires the addition of buffers and minerals supplements before it can be used during replacement water changes. If this water is to be used as replacement for evaporation many add calcium, magnesium, iodide, selenium, and trace elements solutions. However, the big problem for reef tanks is the hobbyists lack of knowledge of high quality water's unique solvent effects. First, high quality, water should have conductivity measured via gold flow cell, on an instrument capable of reading to 0.056µ/S, calibrated by a prepared 25µ/S standard solution. Second, all ultra pure water must be piped sealed through teflon or polypropylene tubing/pipe into a sealed polypropylene storage container. All pipes and storage tanks must be flushed with ultra-pure rated water prior to first usage. If any air contact is made this highly reactive water will be turned into literally waste water. For example: 1.0-2.43 µ/S water will absorb plastizers, VOCs, heavy metals out of most plastics and then absorb any room's undesirable gasses CO, CO2, NH3, O3, N2, VOC's which then produces [5-100µ/S] gas and impurity saturated water. This water will contain: vinyl chloride monomer, epoxides, cyanides, thiocyanides, heavy metals, volatile amines, trihalomethanes, other volatile organic chemicals + CO2 Gas, NH3 Gas & other atmospheric gasseous contaminates. This contaminated water is then dosed with calcium, strontium, selenium, iodide and assorted trace elements before addition to the reef tank. This R/O or D.I. water may also contain heterotrophic bacteria or endotoxins that grew in the filter media. Ref.: Heterotrophic menace: fact or fiction?, Water Technology, Feb. 1999.
BTW for those drinking DI water:
There are two kinds of DI filter cartridges.
The transparent color-change resins are not suitable for drinking water.
Non-colorchange resins are suitable for drinking water.
I myself wouldn't drink DI water.
Carlo
