I think distilled water is overkill, I'm sure my SDL has never seen a drop of it and the cooling system is still clean. My radiator died from old age, it still cooled fine. Unless you live in an area with a lot of crap in the water, like lime in FL for example tap water is fine. Tap water these days is filtered really well.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200