demineralized water - not sterile

[mesenteria]

Let's forget the water for a second.  The air you breathe, about 15 times each minute on average.......................................hour after hour..................................day after day...............................................................

[Mosquitobait]

You don't need to use sterile water. The VA told the guys that the only time they need to boil water for their cpaps is if they are getting water out of open water such as a river or lake because of the flying insects that hatch and the SMALL possibility of bugs riding on the water droplets. Hospitals often make you use sterile water, although tap is just fine, because they want to control what you put into yourself to reduce liability.

[Ron AKA]

Actually, the most pure water is produced by a combination of mixed resin ion exchange and/or reverse osmosis, followed by multi-phase
(multi-effect) distillation. That is how USP water for injection is produced for the production of sterile pharmaceuticals. Even after that treatment it is not sterile. It must be sterilized by passage through sterilizing membrane filters or heated to 250 deg F under 15psi pressure. A less pure grade of water known as USP purified water is produced by ion exchange treatment or reverse osmosis. The best industrial RO systems will produce water as pure as that produced by ion exchange treatment.

You obviously have experience in the water purification industry. I did two reverse osmosis projects later in my career in the power generation industry. The first one used a two stage RO design and was able to produce water with a little better quality than the evaporator (distillation) unit it replaced. The other one was also a two stage unit and was used to pretreat the water feeding a traditional anion, cation, mixed bed ion exchange train. The RO replaced the cation and anion units which required frequent regeneration due to the hard water. It allowed for a staff reduction due to the operator time required for the regens. Water perhaps improved slightly, and the water from the RO only was close to being of the quality required for the boiler pressure in that plant. I have not seen demin trains followed by distillation units, but then I have not worked in the pharmaceutical or semiconductor manufacturing industry. The issue with distillation is preventing physical carryover with the steam if they are pushed too hard. In theory perfect, but in practice, not always...

[Hydrangea]

Good info!

[Melman]

You obviously have experience in the water purification industry. I did two reverse osmosis projects later in my career in the power generation industry. The first one used a two stage RO design and was able to produce water with a little better quality than the evaporator (distillation) unit it replaced. The other one was also a two stage unit and was used to pretreat the water feeding a traditional anion, cation, mixed bed ion exchange train. The RO replaced the cation and anion units which required frequent regeneration due to the hard water. It allowed for a staff reduction due to the operator time required for the regens. Water perhaps improved slightly, and the water from the RO only was close to being of the quality required for the boiler pressure in that plant. I have not seen demin trains followed by distillation units, but then I have not worked in the pharmaceutical or semiconductor manufacturing industry. The issue with distillation is preventing physical carryover with the steam if they are pushed too hard. In theory perfect, but in practice, not always...

Yup. 30 years in a sterile pharmaceutical plant. Pharmaceutical water needs to be more pure than boiler feed water. If your distillation unit was single effect  (only one distillation step) it's not surprising that the two stage RO produced better water. There is always some carryover of minerals and other materials during distillation. To get really high purity water it is necessary to subject the distilled water to multiple sequential distillations. It's more complicated than would interest anyone here. In fact we've probably already bored them to death, LOL.