There's been lots of heated debate on this forum and others on the merits and pitfalls of using distilled water. The talk is about as passionate as what you read in an oil thread.

I believe the debate is in favor of using distilled water when convenient, and staying away from "bad" water such as well water or water from a softener. Though some will point out that distilled water may start stripping metal ions from engine parts, mixed with coolant this phenomenon goes away.

You can access some of the previous discussions with a search using the words "distilled water".

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