I don't think distilled water significantly leaches minerals from anything more so than any other water that has not reached it's saturation point for that particular mineral. I've kept frogs in distilled water for several years before switching to spring water and they've not exhibited any ill effects.
The hype on the internet about it is just that overblown half-truths that originally came from sites that want to sell you their miracle cure for your other ailments.
And the OP was only asking about wetting their coco fiber with it.