Hi h-b, I'm recently getting back into espresso after a long break and recently picked up a Decent. I live in Mammoth Lakes, CA and our water sources are described as follows:

Water provided to MCWD customers comes from both surface water and groundwater sources. Surface water from Lake Mary is
collected, filtered, disinfected, and treated for corrosion control. Groundwater is pumped from nine wells located within the
community in the Mammoth Basin watershed. Water from all but one of the wells is treated with ferric chloride and filtered to
remove iron, manganese, and arsenic prior to delivery to customers. Depending on where you live in the community, you may receive all surface water, all well water, or a combination of the two. The source of your water may also change depending on the season.

This is the utility's water report: https://mcwd.dst.ca.us/wp-content/uploa ... R-2022.pdf. It has pretty wide ranges for TDS etc so I sent off some tap water for analysis from Ward Labs. Here's what I got https://www.dropbox.com/scl/fi/m4h01yz3 ... 2sts1&dl=0. My report is pretty different from the water district's report.

Plugging in my report to the La Marzocco calculator, it reports:

Water Effects on Equipment: Slightly corrosive but non-scale forming
Suggested Water Treatment: Remineralization (with P)

I've been using Crystal Geyser water while waiting, but would it be reasonable to switch to tap water, filtered with a particular filter? Anything else I should be thinking about?

The Ward Labs report looks great, but as you say the Mono County Water District report with those wide ranges raises concerns that with shifting sources your tap water might benefit from some filtration. Unless the chloride levels get higher you shouldn't need to consider RO.

Thanks. The source switching usually happens in the summer/fall (winter/spring is surface water, summer/early fall may include groundwater due to increased irrigation needs), so sounds like as long as I periodically check the water source, I should be OK.

lfranchi wrote:The source switching usually happens in the summer/fall (winter/spring is surface water, summer/early fall may include groundwater due to increased irrigation needs), so sounds like as long as I periodically check the water source, I should be OK.

Agree with that. Your water report looks like one or more of those wells is producing very hard water, but none of them have a high chloride problem. (The ferric chloride treatment uses very little, and the added ferric chloride produces a sediment that is filtered out.)

To keep an eye out for a water source change you can use an inexpensive conductivity 'TDS' meter, typically calibrated on NaCl. The water in your Ward labs sample would read about 35 ppm at 20 25℃, so if you're in that ballpark you can assume that you are on a similar source. If it goes moderately high for short periods I would not worry - your soft water will tend to gradually dissolve any scale deposits. During or after a temporary period of hard water you may want to take steps to drain and flush your steam boiler with purified water.

lfranchi wrote:Plugging in my report to the La Marzocco calculator, it reports:

Water Effects on Equipment: Slightly corrosive but non-scale forming
Suggested Water Treatment: Remineralization (with P)

That calculator is simplistic and a little misleading when it comes to good soft water. I think it's true that it's non scale forming, but disagree that it's corrosive. At your hardness:alkalinity of 23:23 ppm as CaCO3, it's very similar to Seattle water where espresso shops and home baristas do just fine with a particulates plus carbon or charcoal filter. Since your utility uses chlorine, you don't need to spend extra on a special chloramine filter.

Agree that the MCWD report doesn't raise concern for high chloride levels throughout most of the year. I lived in the area years ago and the water quality was very good. My concern regards the fact that during heavy snowfall in the winter months the higher elevation roads in eastern sierra, especially around Mammoth Lakes, may be salted. This would transiently increase the chloride in runoff water and over time get into well water. This would be a seasonal, not a year round problem, and could be dealt with by determining when a spike in chloride level occurs and switching to using the reservoir during those times.

Oh, the salting of the roads and thus salt runoff is a fascinating point I hadn't even considered! Winters aren't going to get much bigger than this past winter (hopefully...) so I imagine this spring/summer's runoff was about as much as we'll see.