A few others I have chatted with have used a similar system as below.
EDIT - JULY 2020 - Have now used this flawlessly for 16 months and highly recommend it. You can either use RO water without materialization or distilled water. This system is particularly great if you have high chlorides (different than chlorine). If you use an RO to feed your tank, you will want to get a flow measurement device to know how much buffer and hardness stock you want to add. I have collected my learnings on this forum and happy to share them if you PM me with an email address.
Sorry about some the image sizes.
The set up is: Holding tank>check valve>pump>accumulation tank>pressure regulator>espresso machine
Here is the final product on the cart. Note the wide mouth on the tank makes filling easy. The waste tank has a handle which makes it easy to carry out to the garden and dump.
Holding Tank - 6 gallon rectangular tank. July 2020 edit notes. I find this tank really needs to be refilled with four gallons as the exit point is not at the very bottom of the tank. Four gallons lasts about three weeks for 4-6 espressos a day plus cleaning routines. Note the wide mouth opening makes refilling very easy.
https://www.usplastic.com/catalog/item. ... mid=125271
I am considering replacing the tank with this larger one which would fit my space although the opening is only 4" and not 5".
https://www.usplastic.com/catalog/item. ... &catid=835
To use the Holding Tank with JG 3/8 tube you will need a reducer bushing of some sort and JG adapter. I chose the following. You might want to base your decision for the reducer on whether you can buy a single (rather than a pack of 10) JG adapter.
-Reducer Bushing 3/4" NPT Male x 1/2" NPT Female
- John Guest ½ NPTF Straight Adapter 3/8 OD tubing
PP011224W 3/8" 1/2"
Check Valve to prevent backflow when refilling tank. [Not sure this is necessary but is nice to have so I don't have to turn the shut off valve]
https://www.freshwatersystems.com/produ ... k-pressure
Pump
Aquatec 5853-7E12-J524 1.7 GPM 60 PSI 3/8 inch JG 120V Delivery/Demand Pump with Cord.
https://www.amazon.com/dp/B008GNFN82/
Accumulator - with a John Guest 3/8 adapter on top connects into pump line with a T.
https://www.freshwatersystems.com/produ ... nk-3-2-gal
J Guest Valve for Accumulator
https://www.freshwatersystems.com/produ ... x-1-4-nptf
John Guest T - one side to pump and other side to pressure regulator before espresso machine with T too accumulator
https://www.freshwatersystems.com/produ ... olypro-3-8
Pressure regulator
https://www.chriscoffee.com/Pressure-Re ... /334gg.htm
For more precision at more cost consider a Swagelok pressure gauge.
Waste Container
https://www.amazon.com/LCI-Plastic-Wate ... 828&sr=8-1