Distilled and tap water ratio for optimal taste vs. scale

[Grant]

Anyone have an approximate/optimal ratio of distilled water to add to tap water (let's assume 200ppm hardness) for preventing scale vs. taste?

I have a client that has a distilled water tap directly beside his tank espresso machine. Almost 100% milk based drinks, so mixing for scale reduction probably a bit higher priority than optimal taste.

Any thoughts on what has worked for you?

Grant

[cannonfodder]

If you are running a HX machine, you could fill the boiler completely with distilled water since it will not be used in the brewing process. Then the normal tap water can feed the HX, although 200ppm is darn hard. 100-110ppm is about perfect if I remember Jims insanely long water FAQ, so a softener may be needed.

[another_jim]

You need 50 ppm hardness water to be boiler safe (although the best taste is at around 90 ppm). If the water is at 200, you are looking at 3 parts distilled to 1 part tap -- unless they have distilled to spare (i.e a table top still running at low capacity), a softener is cheaper.