If you're only interested in the bottom line...

Use Volvic or Crystal Geyser Natural Alpine water in your home espresso machine. They have formulations that won't scale, but which still taste OK for coffee. On the other hand, if you want to take some pains and save some money, read on.

Content Note

The alt.coffee archives have answered almost all my coffee questions. However, the coverage on water problems seemed a little less than complete. So I'm adding this bit of research as a small repayment for all the help I've gotten here. It's too long to read in one sitting, so copy and peruse it at your leisure. Headings and subheadings are in block capitals; you can find what you need by scrolling through. There are several tables, so use a fixed pitch font.

This is not meant to be the authoritative word on water quality for coffee, I don't have nearly the expertise for that. I'm hoping to acquaint readers with enough information and sources so that we can argue water matters as proficiently as other coffee issues. There are bound to be mistakes in here, so I welcome all corrections. This FAQ covers the effect of minerals in natural waters on coffee taste and coffee makers. It has four sections. The long first one explains how to measure scale related water properties and how to estimate scaling rates in espresso machines based on these. The second looks at water treatments. The third taste tests espressos made with variously treated waters. The fourth puts together the conclusions of the first three and outlines water treatment and descaling options.

The FAQ does not discuss water impurities such as chlorine, organic materials, or heavy metals, since they shouldn't be in any drinking water, and since they're removed by all water bottlers, reputable types of water filtration, and municipal water boards. Municipal levels of chlorine are removed by charcoal filtration, letting the water stand two hours, or heating it. If your waterboard uses chloramines for disinfection, the water should be charcoal filtered prior to taste sensitive food use, since these do not dissipate on their own.

1. How to Measure Water Properties and Estimate Scaling Rates

   1. Water Hardness Defined

      Hardness is the term for the calcium or magnesium carbonate dissolved in water as Ca++, Mg++, and HCO3- (bicarbonate) ions. There are two measures of water hardness, hardness and alkalinity. Hardness measures the amount of positive calcium and magnesium ions; alkalinity the negative bicarbonate ions. Both measures are usually given in calcium carbonate, i.e. scale, equivalent units (abbreviated as CaCO3). This means when one unit of scale precipitates out of the water, hardness and alkalinity measured in CaCO3 units go down by one unit each.

      Alkalinity and hardness levels need not be the same, since the bicarbonates can be associated with potassium or sodium, and the calcium or magnesium with chlorides or sulphates. Usually, alkalinity is less than hardness, although some mineral waters and ion exchange softened waters rich in sodium or potassium may have higher levels of alkalinity.

      Sometimes alkalinity is called "temporary" or "carbonate" hardness, the difference between hardness and alkalinity, "permanent hardness", and the hardness itself, "total" or "general" hardness. This usage is common among aquarium owners, but does not accurately convey how scaling works.

      There are no health hazards associated with water hardness, so it is not subject to regulation. However, hard water causes scale, as well as the scumming and reduced lathering of soaps. Very soft waters, exposed to air or heat, become acidic and corrosive, and can harshen the taste of vegetables, tea, or coffee. So, several countries including the US, UK, Canada, and Germany have issued non-binding recommended hardness ranges. These are usually aroung 80 to 100mg/l hardness and 50 to 60 mg/l alkalinity, figures calculated to minimize the combined cost of scaling and corrosion in municipal piping and domestic hotwater systems. The levels required for taste, or for low maintenance steam boiler, spa, or aquarium operation, can be quite different.

      Water boards call waters in the recommended range "neutral," those below the recommended range are called "moderately soft," below half the range, "very soft," above the range "moderately hard", and above twice the range "very hard." However, the exact ranges referred to by these names varies, and one should always get the exact water analysis.

   2. Limescale Precipitation, pHs & the Langelier Index

      Whether and how much scale precipitates depends on the water's alkalinity, hardness, temperature, and total dissolved solids. These factors together define a quantity called pH at saturation, or pHs. pHs indicates the pH level at which the measured calcium/magnesium bicarbonate level is at equilibrium saturation. If the pHs exceeds the water's actual pH, no scale will form, in fact, existing scales will tend to dissolve into the water. This is how the hardness gets there in the first place, and why descalers are acids. If the pHs is less than the actual pH, lime will precipitate out of the water until the pH balance is restored.

      The formula for pHs is as follows: The logs are base 10, T is temperature in centigrade, S is mg/l total dissolved solids, H is mg/l hardness, and A is mg/l alkalinity, both stated in CaCO3 equivalent units.

      pHs = 44.15 + log(S)/10 - 13.12*log(T + 273) - log(H) - log(A)

      The quantity pH - pHs is called the Langelier Index or LI (sometimes called the Saturation Index or SI). A negative LI means no scaling, a positive one means scale will form. The LI formula is:

      LI = pH + 13.12*log(T + 273) + log(H) + log(A) - log(S)/10 - 44.15

       

   3. Water Analyses and Testing

      Water authorities must publish their waters' composition, and many put up the analyses on municipal websites. Bottled waters also will provide a complete water analysis on request. Many bottlers state the composition of their water at this web site: http://www.bottledwaterweb.com/bott/ Unfortunately, some don't, and some analyses are incomplete.

      Mineral levels are stated in a number of different measurement units: milligrams per liter (mg/l) is standard. Parts per million (ppm), and the milligrams per decimeter cubed (mg/dM3) used by MKS fanatics, are identical to mg/l. French degrees is mg/l divided by 10. Grains per US gallon is mg/l divided by 17.2. English degrees is mg/l divided by 14.3 (grains per Imperial gallon). German degrees (DH) or mmeq/l (the ueberscientific millimoles equivalent per liter) is mg/l divided by 17.9. Feel free to invent your own unit and add it here.

      Finally, bottled waters mostly report their minerals as straight elemental mg/l or ppm rather than mg/l CaCO3 equivalents. To get the alkalinity, multiply the bicarbonate by 0.82; to get hardness multiply the calcium by 2.5, the magnesium by 4.2, and add the two. If the water is fizzy, and bicarbonate level isn't stated; the alkalinity will equal the hardness after the water goes flat. 

 Read the entire article at: http://www.big-rick.com/coffee/waterfaq.html