My problem is a high pH in the boiler water of my Bezzera Strega. I have it plumbed in with a sediment pre-filter then a water softener ( DVA model iV12 ) then a 0.5 micron carbon filter to a pressure regulating valve and finally to the Strega. I'm using Nutrafin aquarium water test kits for GH, KH and pH testing. The ph testing kit range is 4.5 to 9.0 pH. I last tested the city water at GH 140 ppm, KH 70 ppm and pH at 7.5. The water out of my softener tested at GH 20 to 40 ppm, KH 70 ppm and pH at 7.5. The boiler water continually climbs to the maximum range of the test kit 9.0 and may even be higher but that's the limit of my test kit. Flushing a few cups of water from the boiler daily does not help, I have to drain the boiler completely and flush it a few times but the high pH returns and the boiler water starts to get a reddish brown tinge ( tea like ) which gets darker if I don't flush the boiler. Obviously I'm concerned about corrosion in the copper boiler ( high alkalinity can be as corrosive as high acidity ). It doesn't seem normal that this is occurring as quickly as it does. This past Sunday I flushed the boiler about 3 times and checked the pH to be 7.0. Monday I tested it to be 7.5 and by Tuesday it was 9.0 again but the water appeared to be still clear. Can one of the chemists here please explain in simple terms what's happening and if there is anything I can do to mitigate this. Thanks.

The problem with using standard water softening systems is that they increase sodium ion concentration, and also any chloride that gets retained during the recharge system becomes a contaminant. Chloride ion complexes copper and facilitates oxidation by air. (Contrary to the ideas of some, the electrode potential for copper is extremely unfavourable for reaction with water. Copper corrosion is caused by OXYGEN.) Copper forms a fairly durable dark coloured oxide coat that is most stable at about pH 7.8 or so. When water gets either acid or alkaline the oxide coat can go into solution and allow the oxygen to get at the copper. In addition in alkaline solution hydroxide absorption on the metal surface facilitates oxidation by molecular oxygen because the negative charge of the hydroxide ion increases surface electron density.

You do NOT want chloride in the water because both cuprous and cupric chlorides are complexed by chloride.

Is there some sort of sacrificial anode in the system?

I think you would be better off with some sort of reverse osmosis system.

Are you sure that there is not some sort of iron object that got into the system? Iron objects in contact with copper tends to make water that looks like tea quite rapidly from suspended hydrous iron oxide.

Thank you for the reply Robert. After reading your point "You do NOT want chloride in the water because both cuprous and cupric chlorides are complexed by chloride" , I'm wondering if this additional information might help.
When I first bought the softener I was concerned about the added sodium to the already high salt, north american diet. I initially charged the softener with potassium chloride but found the water to have an unpleasant taste. It probably was my inexperience with the softener and I may have just not rinsed the resin enough when first commissioning it or I may not have rinsed enough after charging it with the potassium chloride. In any case I wasn't happy with the taste so I flushed the softener for a while ( but no where near its capacity, which is 2520 litres at a hardness of 200 ppm CaCO ) and then recharged it with salt.
Is it possible charging the resin with both potassium chloride and sodium chloride has caused this? Please excuse if this sounds totally silly but I'm no chemist. Thanks again for any help.

It really should not matter whether sodium or potassium chloride be used to recharge water ion exchange resins, except one will have most of the cations replaced with sodium and the other potassium. The Na or K ion concentration in softened water is appreciable. Any chloride that remains from the recharge is a very bad thing to have present because high concentrations of it will stabilise cuprous ion that is seriously catalytic for air oxidation of copper. It can give rise to what is called "red bronze disease" and serious pitting that can ultimately destroy various copper alloys. (Brass is simply zinc bronze, and is highly subject to this.)

There are massive concentrations of potassium in brewed coffee, so if you can taste the result of more potassium you must really have high concentrations. There is about 2% potassium in coffee beans and a large fraction of this gets extracted into brewed coffee. There is also about 0.2 to 0.25% Calcium and magnesium in the beans themselves. There is also about 0.02% sodium and rubidium. Often there is actually more rubidium than sodium.

Some espresso machines are designed in ways that makes them particularly susceptable to chloride induced corrosion.

High ion concentration in water also enhances dissimilar metal corrosion, regardless of the ion, because almost all of the conductivity of impure water is due to ion migration. There are a very few types of anions that help produce an inert microlayer to protect underlying metal. Tiny concentrations of phosphate protects many metals, including copper, this way. Bicarbonate seems to protect brass. It also tends to buffer pH to near the level of maximum stability of the oxide coat of copper.

Robert it took me a while to find out what the levels of chloride and sulphate are in our municipal water. It didn't list those two items in their posted annual report. It is:

PARAMETER AVERAGE MAX MIN
Chloride 20.4 ppm 24.1 ppm 18.5 ppm
Sulphate 35.6 ppm 40.0 ppm 32.0 ppm

Can you tell me if this is high or low and if this is causing my problem?
Thanks for your help.

Your municipal water does not seem to have excessive levels of chloride or sulphate. I hope that you are not adding more chloride from the softener recharge.

It is amazing how fast water can begin to look brownish from having small amounts of iron in contact with copper inside a copper boiler. I once purchased a 1978 La Pavoni Europiccola whose former owner obviously used seriously sulphate contaminated water. Calcium sulphate scale does not dissolve in weak acids like the carbonate does. Anyway he had somehow gotten an M6 nut in the boiler. Once I got rid of the calcium sulphate scale by using purified water for daily espresso for several weeks, the water suddenly began turning brown overnight. That is when I noticed the M6 steel nut! I removed it and no more brown water. The calcium sulphate scale prevented electrical contact until I got the CaSO₄ removed. Then we had severe dissimilar metal corrosion on the nut!

Water will become alkaline if there be some sort of metal being oxidised to produce a soluble hydroxide. This still might suggest some sort of sacrificial metal rod in the system to prevent corrosion.