The chemist in me reads this and it makes my hair stand on end.
I know this has been thoroughly hashed out, but anything that DI/distilled water "leeches" will come to equilibrium quickly and it just stops happening for all intents and purpose.
As another general comment, at my last job(where I spent 10 years) we had a "house" DI water system that delivered better than 1MΩ/cm purity. Actually I should say we didn't routinely monitor it, we just had a simple go/no go light that told us when it went below 1MΩ, which told us to change the resins(or really call Culligan to come out and do it). Every few months, I'd sample it throughout the building, and I'd routinely measure 1.1-1.5MΩ/cm.
The plumbing for that system was mostly HDPE fittings running through plastic tubing. I'm not sure what type of tubing it was, and that's something I should know. During normal use, a pump circulated water constantly through the system and resin beds, with tap water feeding in as needed. I periodically inspected the system all through the building, some 1500 feet of tubing per my calculations, and never observed any cause for concern.
A few labs had their own ultra high purity water system, which used ion exchange and carbon filtering to scrub the house DI water down to a target 18.1MΩ/cm resistivity, and then do a final output through typically a 5µm filter. If I actually saw a system read that value, I'd tell them they needed to service it, as normally the best a system could do was ~16-17MΩ, and readings up into the 18 range typically meant bacteria or other contaminants on the electrodes in the conductivity flow cell(and it's amazing how many PhD chemists would complain when their freshly serviced system was "worse" than before service and couldn't comprehend why it would read artificially high, but that's another discussion). When I was in graduate school, I used one particular long-in-the-tooth Millipore system daily. That was water you used if you had a real need for it, even though a lot of people in my lab would use it for everything out of habit. It could do funny things if you let it. Many parts of the system were HDPE, but it also had a whole lot of teflon.