GC7 wrote:My method is to make a 1:1000 concentrated solution that I store in a jar in the refrigerator.
20 grams of potassium bicarbonate into 200 ml. of water. It dissolves easily.
I then add 3.8 ml of concentrate into a gallon of water using a pipette. If you don't have lab pipettes I/m sure a 5 cc syringe would work to get ~ 4 ml concentrate. The concentrate lasts quite while.

IMHO this is the easiest way to make rpavlis water, because measuring volume is easier than weighing.

My concentrate is 500x:
Dissolve either 5.0g KHCO3 (potassium bicarbonate) or 4.2g NaHCO3 (sodium bicarbonate, i.e. baking soda) in 100ml pure water (distilled). Store concentrate in refrigerator.

Add 1-2ml of concentrate per liter of pure water for use in your espresso machine, depending on whether you prefer the half or full strength Pavlis formula. I (re)use a 3ml disposable pipette to add the concentrate.

Thanks homebererro. I'm on Vancouver's city water system. Nice to know that it's machine friendly. After running a descale solution through the 2nd machine I remember white bits in the drip tray. I assumed it was scale; what else might it be? Also, what factors other than scale could be responsible for the solenoid failures? I did have, and fixed, a leaky water connection on the top of the main boiler. Could that result in solenoid corrosion and failure?

Hopefully not beating a dead horse here, but this thread came so close to answering my current question. I upgraded my machine and want to switch from bottled spring to refillable RO sourced from my local grocery store (lower cost, lower plastic waste, more convenient, and more consistent TDS). Can I make rpavlis water starting with RO? The RO water I source reads about 10 TDS on a cheap meter, so not as "pure" as distilled. I was considering mixing filtered tap back into the RO, but I notice the effectiveness of the filter changes dramatically over its short lifespan. Thanks all for this incredibly informative Q&A.

858 wrote:Can I make rpavlis water starting with RO? The RO water I source reads about 10 TDS on a cheap meter, so not as "pure" as distilled.

Yes, RO will do fine here. Sometimes those kiosk vending systems are not well maintained, so you can use that TDS meter to keep an eye on that. Some machines sell de-ionized for the same price as RO, and that would be best for use in recipes but is not necessary where the plain RO comes out this pure.

Awesome, thank you! I will monitor each batch I get now just to be sure.

I just use a scale that can read hundredths of a gram and weigh out the proper amount of potassium bicarbonate, add it to the water and shake.

I too find this easier than adding 3.8 grams of the mixture.

mdmvrockford wrote:IF I had a milligram scale THEN I would do what you do. But I am frugal (i.e. cheap) and have the <$20 recommended scale from Amazon that does not measure to milligram. Hence I use concentrate which I then add to 3.78L (1 gallon of distilled water). I test the water with cheap TDS meter and values are in ballpark of 100mg potassium bicarbonate per litre distilled water (and chemistry confirmed by "homeburrero" on prior water thread post).

I looked through this entire thread and I don't see that you prior posted which milligram scale from amazon you use. If you don't mind please post uri to your milligram scale for me and others. I see at least three and would prefer to buy one that is semi-durable and has worked well for others (e.g. you).

I work at an environmental laboratory, and when it comes to weighing dry reagents on a scale, the humidity in the air is a problem. Unless you keep the dry KHCO3 in a desiccator, whenever you weigh some, you're actually weighing less dry material than you think. But of course, this only matters if you're aiming to be very precise. I prefer to make my own stock solution and add it to deionized water to be more consistent. 10g of KHCO3 dissolved in 1000ml of DI water, and I add 25 ml (or 5 US tablespoon) of this stock solution into 2500ml of DI, which is just the right amount for the tank if my Breville Dual Boiler.

cuizable wrote:when it comes to weighing dry reagents on a scale, the humidity in the air is a problem. Unless you keep the dry KHCO3 in a desiccator, whenever you weigh some, you're actually weighing less dry material than you think. But of course, this only matters if you're aiming to be very precise.

Interesting. Never thought of that. In your experience, does this makes a substantial difference when you're weighing milligrams? Or does the moisture issue come into play more when you're measuring units smaller than milligrams?

cuizable wrote:Unless you keep the dry KHCO3 in a desiccator, whenever you weigh some, you're actually weighing less dry material than you think. But of course, this only matters if you're aiming to be very precise.

A while back I wondered about that, especially when I noticed that my potassium bicarb got hard lumps after it had been repeatedly opened for a while. So I tried weighing some of my lumpy KHCO3, dehydrating in a 400F kitchen oven, then reweighing. Mine had gained less than 5% from moisture, which was not enough for me to worry about. Whether you're weighing small or large amounts, the percentage that you might be off due to moisture gain would be the same.

Note- this oven baking method to estimate moisture gain makes sense for potassium bicarbonate or sodium bicarbonate, but would not do for minerals that form hydrates. Epsom salt is an example. It typically exists as a magnesium sulfate heptahydrate, but will tend towards anhydrous if you were to bake it in a hot oven, and the mass difference is significant -- The heptahydrate weighs just over twice as much as the same molar amount of anhydrous magnesium sulfate. One reason people favor Epsom salt over anhydrous magnesium sulfate as a brew water additive is the fact that you don't need to store it in a dessicator. It's also cheap and available.