A thought just occurred to me. Is it worth it to think to correct for the amount of water loss due to evaporation in water tank. I used to wash my reservoir every two weeks. But with the potassium bicarb, I now need to wash it monthly (the potassium bicarb does a good job of preventing slimy bacteria growth). But over time, water will evaporate as the reservoir is not air tight. Over time, as more water evaporates, the concentration of potassium bicarb will increase. But perhaps this evaporation effect on the potassium bicarb concentration is negligible. Just wanted to hear people's thoughts.

Interesting question, I had not thought much about that but I'll be curious to see what others think. My initial take is that yes, there will be a slight concentration over time due to the evaporation. If you top up your reservoir after every shot then you'd increase the level of concentration whereas if you wait until the level in the tank drops then you'd be topping up with a larger volume of correctly mineralized water therefore reducing the effect by diluting the water with [slightly] elevated levels of potassium carbonate with the water you want.

Good news is that this is not something unique to R Palvis or any other water recipe for that matter, as the same exact thing would happen in you were simply using tap water.

My guess is that the effect would be negligible however if you wait until the tank level drops to half or maybe a bit under prior to topping off then it would be even more negligible.

I'd suggest eliminating the recurring slime growth.

I would remove the reservoir and soak it (and the jug that you use to refill the reservoir) in 50:50 vinegar:hot water, and then rinse thoroughly with hot water. Also, unplug the machine, and wipe down the area around the reservoir and the bottom of the machine's lid with a cloth dampened with the 50:50 solution (and then wipe down again with just hot water dampening another cloth). You want to kill all the spores.

I don't know your machine, but if the water reservoir is placed such that the water in it heats up, then you might also want to consider insulating the reservoir.

As for evaporation, it shouldn't be a concern unless you let the machine sit unused for many months ... in which case the reservoir should be emptied out anyway.

baldheadracing wrote:As for evaporation, it shouldn't be a concern unless you let the machine sit unused for many months ... in which case the reservoir should be emptied out anyway.

I agree. A typical reservoir with an open top is only going to lose 10 - 100 ml/day due to evaporation. Even if you're adding only 500 ml/day to the tank you are looking at a max concentration factor of 1.02 to 1.25 -- not enough to worry about.

Most important job is to periodically empty and clean that reservoir; the water in there generally has no chlorine or chloramine disinfectant. And if making water from purified water you want to also periodically clean your containers that you use to mix and store your concentrates and brew water. It also would be good to store those in a cool dark location.

My question was more about the evaporation loss, and not so much about "slimy" bacteria growth. I really don't have an issue with bacteria. I used to religiously wash my reservoir with hot soapy water every two weeks when I was using Gerber Pure. At the two week mark, I noticed that the inside of my reservoir was just starting to get a little slippery. When I switched to R Pavlis water, I noticed that that wasn't the case, and that even after letting my water sit in the reservoir (which is enclosed in my machine) for a month, there was no slippery feel to the inside and the water tasted just as fine as when I just did a wash. My machine has always been downstairs, which is substantially cooler than the rest of the house, and in the winter it cruises down here in the low 60s.

I'm not having an issue with bacteria, my question was about the concentration changing due to constant evaporation as I've never seen anyone discuss the issue. And if we're talking about measurements in small increments like milligrams, the effects water evaporation might come into play over time. Obviously any concentration differential would be eliminated when I do my monthly washing and refill, but I was wondering about the effect after say two or three weeks or so.

And I just put 100 mg of potassium bicarb directly into a liter of distilled water (poured straight from the gallon jug I buy it in) whenever I need more water.

Sideshow wrote:My question was more about the evaporation loss, and not so much about "slimy" bacteria growth. I really don't have an issue with bacteria.

Sorry for digressing into that issue. It's been on my mind lately because of recent discussions related to home-made water recipes, including rpavlis, somehow fouling the PID sensors of LeLit machines.

Sideshow wrote:... my question was about the concentration changing due to constant evaporation as I've never seen anyone discuss the issue. And if we're talking about measurements in small increments like milligrams, the effects water evaporation might come into play over time. Obviously any concentration differential would be eliminated when I do my monthly washing and refill, but I was wondering about the effect after say two or three weeks or so.

My little back of napkin calculation above was an estimate of the concentration factor you might expect after an infinite period of time. It's based on the standard formula used for concentration effect in steam boilers:

Jim Schulman's Insanely Long Water FAQ wrote:Actual mineral concentrations in the boiler, if saturation isn't reached, depend on the ratio of steam to water extraction and is as follows:
Boiler Concentration = Feedwater Concentration/(1 - Steam Ratio)

So in this case assume that you put 500ml of water into the reservoir every day, and that 100ml of that water evaporates in a day. So then:
reservoir concentration = feedwater concentration / (1 - 100/500) = 1.2 * feedwater concentration.

In practice, even with a 3" x 8" open reservoir with warm dry air circulating above it you probably would not lose 100 ml/day to evaporation, so that concentration factor would be a high estimate.

I took a thin silicone baking liner and cut it to fit over the top lip of my water tank (under the stainless steel door on the top of my machine) to minimize the evaporation.
It seems to work well as when I open up the top door, there is never any condensation on the underside of the door but there is always condensation on the underside of the silicone baking sheet. My thought is that it will contain the condensation and as it accumulates it will just drip back into the reservoir.

Josh