I am currently using nestle purelife bottled water for espresso which marks 3 grains hardness using hach 5b test kit. How often should I descale my espresso machine using this water?

Normally to get help with that question you would need to provide the alkalinity numbers as well as hardness, plus how much water you run through the machine's boilers as well as the boiler temperatures. Here's the bible with respect to doing your own scaling estimates: Jim Schulman's Insanely Long Water FAQ.

In the case of Nestle Pure Life you can get information online: https://www.nestle-watersna.com/asset-l ... pl_eng.pdf
Their water with added minerals, which I bet you are using, has low hardness and very low alkalinity, so most of the hardness is non-carbonate. It won't deposit scale even if you run a lot of water through a high temp steam boiler.

They are adding that small amount of hardness minerals in the form of non-scaling chlorides and sulfates. There is an arguable downside to that - the low alkalinity (10 - 17 mg/L) combined with about 14 - 19 mg/L chloride is less than ideal with respect to corrosion risks.

So there is a possibility that it will corrode my machine?

Also if i felt inclined to keep using this water, what kind of treatment(epsom,bicarb?) do you recommend to make it suitable for espresso? Thanks much in advance!

akirapuff wrote:So there is a possibility that it will corrode my machine?

Possibility yes, because corrosion experts say that any chloride may be harmful and the current advice about alkalinity is to keep it up near 40 mg/L - but that water is not seriously bad and any corrosion may take a long while. That water is similar to the Gerber Pure remineralized baby water that is relatively popular for use in espresso machines and we haven't heard negative reports about that. (Gerber Pure has slightly better alkalinity and slightly worse chloride than this remineralized Pure Life water.)

akirapuff wrote:Also if i felt inclined to keep using this water, what kind of treatment(epsom,bicarb?) do you recommend to make it suitable for espresso? Thanks much in advance!

A simple bicarbonate spike would help.

You'll see many references in this forum to "rpavlis water" which refers to chemistry professor Robert Pavlis' water recipe. (HB member rpavlis, RIP) -- which is purified or distilled water spiked with 50-100 mg/l of potassium bicarbonate.
From 1977 La Pavoni Europiccola with green deposits/scale :

rpavlis, in linked post above wrote: .... I personally use, as I have stated many times, about 0.5 to 1.0 mMolar potassium bicarbonate. You can simply add from 250 to 500 milligrams of potassium bicarbonate to a 5 litre container. You can use sodium bicarbonate too, but I do not like doing that because it seems to create peculiar flavours because Na is very low in coffee beans.

An easy way to make it up is to make a bottle of concentrate: Get a 750 ml stoppered bottle, add 9.6 gram of potassium bicarb to that, fill with water and shake well. Then for every US gallon of purified water just add 1 to 2 tablespoons of that concentrate. (1 tablespoon works out to 0.5 mMolar bicarbonate -- or a total alkalinity bump of 25 mg/L as CaCO3.) If you go with sodium bicarbonate (baking soda) you would use a little less - about 8.1 g instead of 9.6 g in the concentrate bottle.

If you used distilled or the non-mineral version of Nestle Pure Life it should be best because of having zero chloride, but this recipe would nicely fix the low alkalinity in the water you already have.

do you recommend the same recipe for the distilled version?

Yes. If you go with 2 tablespoons (30 ml) of that concentrate in a gallon of distilled you're at the 1 mmol/L potassium bicarb water that was oft recommended by Dr Pavlis. (Total alkalinity of 50 mg/L as CaCO3 and zero hardness.) He said he would sometimes use only half that amount of bicarbonate for taste reasons when brewing dark roasts.

Where can you buy potassium bicarbonate? Google directs me to wine purveyers. Is there a brand or a source you trust? Also is baking soda just as good? Or does it have any downsides compared to potassium bicarbonate? Thanks in advance!

Its my understanding that people who make their own wine or beer do use potassium bicarbonate. So your local brewer supply store would be ok. I bought mine off of Amazon though. Baking Soda would have sodium... see earlier in the thread about sodium in coffee.

akirapuff wrote:Where can you buy potassium bicarbonate? Google directs me to wine purveyers. Is there a brand or a source you trust? Also is baking soda just as good? Or does it have any downsides compared to potassium bicarbonate? Thanks in advance!

https://smile.amazon.com/Home-Brew-Ohio ... 131&sr=1-4