I read something recently that suggested some of the high resistance in ultrapure water was due to dissolved gases. When these gases were removed, it was more like 5 MegaOhms.
I’m speaking from memory, and have no cite. We use 18.6 MegaOhm water in our lab.
Resistivity is commonly given in ohm-cm, not ohm/cm. This is known as “volumetric” as you can derive the resistance based on a given volume. You would take this value and multiply by the length, since length increases resistance. Then you divide by the cross-sectional area, as more area decreases resistance. Technically measured values are probably defined on a standard volume at a specific temperature as well.
And of course it’s not uncommon to incompletely specify the units when everyone knows what they signify (as in the 18.6 Megaohm figure WarmnPrickly gave).
Referring to all water as conductive to a degree isn’t a problem in itself, as long as you understand it apples to every material. By this reckoning, insulating materials do not exist. I’m not trying to be facetious either; it can be useful to remember what can happen under the right circumstances.