Zero Water makes water filtration systems that they claim remove 99% of total dissolved solids from water.
On the Water is the New Gold blog, a water-filter scientist warns against its use:
More dangerous is the fact that the Zero Water Filter removes 100% of the chlorine form the water. [...] Bacteria will grow in water that has no chlorine in it. [...] Also remember, ion-exchange resin is also a great medium for growing bacteria.
Will water filtered this way act as a harbor for bacteria?
Daschner 1996 gave a look into ion exchange filters - it was devastating: "In 4 of 6 filters tested in the laboratory, bacterial counts in the fresh filtrate were higher than in tap water after approximately one week of use both at room temperature and at 4°C, suggesting growth or biofilm formation in the filter material. In some cases colony counts in the filtered water were 10,000 times those in tap water. The filter material of 5 of 13 new commercial filters was contaminated with bacteria or moulds."
As Zero water only makes claims about he removal of stuff ("dissolved solids" - aka the stuff that we pay for in mineral water), the (re-)introduction of stuff is (wisely) not covered in their marketing material. As the ion-exchange filter will work fine on chlorine, if the water was devoid of bacteria before, and safe against the introduction of microorganisms via added chlorine, after filtering the water will have added bacteria and fungi, and no chlorine to counteract. Cool trade.
