Reverse Osmosis

Reverse Osmosis & Coffee Machines

In this article, I want to describe how I am using Reverse Osmosis (RO) to keep my machine in good condition and optimise the taste of the coffee. I will also cover how to go about obtaining an RO system, typical costs and installation hassles.

The 3 main reasons I am using RO?

  1. It's better for my family to drink (reduction in pesticides and other contaminants)
  2. It's better for my expensive coffee machine (with no descale hassles)
  3. Drinks including coffee taste better (especially without all the other unwanted compounds, fluorine, chlorine, rust, sediment etc…)

I had considered installing a standalone RO system, but research showed that these systems actually worked even better using softened water, I was having new bathrooms installed, so decided to have a water softener installed and use the RO system on softened water, as shall be seen later, this is actually a big plus. So I went ahead and had a water softener fitted…so far so good.

The next step was the choice of RO system

There are a number of different systems on the market and you will need to research what best suits your situation. The split into those with and without storage tanks and with or without booster pumps. I believe there are some counter-top RO systems available, but they are quite expensive. These (as the name implies) simply sit on the counter-top, you fill a chamber with water and a small pump runs it through an RO membrane, they need no plumbing (but of course do create waste water and this needs to be vented via a hose. I decided on a 5 stage pumped system with storage tank, as it also needed to supply drinking water for the whole family.


You will need to plumb it in and you can get a plumber to do this, or if you are a competent DIY’er, then it’s not hard to do yourself. You will loose about 70% of a 600M kitchen cupboard to do this and it needs to be sited reasonably near to the waste water drain…hence the best location is under the kitchen sink. The units are widely available and can cost from £50-£110 for a basic to pumped version. I bought mine from an firm called VYAIR who sell on the Internet direct from their web site. The prices are good and the kit is high quality.

A slight problem with RO water, is that it can be slightly more reactive than tap water, apparently corroding the very thin copper tubing sometimes used on fridge water supplies, this behaviour is not peculiar to the RO process and all “pure” water will exhibit this phenomenon. I don’t think you would have a problem with coffee machines….but better to be safe than sorry.
To counter this and also to improve the taste (because of the slight increase in bitterness (mainly due to the reduction in dissolved calcium), I actually add Sodium Bicarb to my RO water, this brings the TDS up to an ideal level for coffee making, with no risk of scaling or copper leeching see ro-water-copper-corrosion…..and no descaling required.

For Americanos, I simply use all RO water in my Kettle, as I use sugar in americanos (but not in espresso), so couldn’t care less about any effect on bitterness.

You could also add a proportion of softened water if you wish, not as effective, but it helps.
Softened water if you remember has the calcium ions exchanged for sodium ions. This gives me an effective ppm of Total Dissolved Solids (TDS) of around 60-70 ppm. Worked out as follows:

TDS Softened water from the Tap = 350 ppm
TDS RO water = 10 ppm

17% of 350 ppm TAP water = 59.5 ppm
83% of 10 ppm RO water = 8.3 ppm
When Mixed giving a TDS of 67.8 ppm

Now if you don’t have softened water, you can still mix the hard tap water in with the RO water in the same proportions. This again will greatly reduce the amount of descaling required….but you will still have to descale. E.g. if you needed to descale once every 3 months before. Using RO water+17% hard tap water, you may only have to descale the brew pathway every 15-18 months and if you don’t use the machines boiler as a kettle, then the main boiler will not have to be descaled very often at all, possibly once every few years.

In both scenarios though (whether you mix with soft or hard water)….you should on a monthly basis refresh the water in the steam boiler and refill it, this is best achieved by bringing the machine up to temp, switching off, opening the hot water tap and draining as much water out as you can. If you have a machine such as a La Spaziale, which uses electrovalves to control hot water flow, then you will have to drain via the boiler drain nut on the S1 MKII and on the Mini Vivaldi, remove a boiler fitting and use a syringe and plastic tube to drain the (COLD) boiler (because if doesn’t have a drain nut)

If you did go for a water softener, just remember that they need to be kept clean, use good quality salt, and also over time they get contaminated with iron compounds and the resin bed becomes much less effective….this can take many years (8-12 years). It’s not well known, but if this happens, a citric acid soak and flush actually revives the resin bed and links with the Iron to drag it off the resin (so you do still have a use for that descaler). The observant among you will also realise that you can use this technique to revive the resin bed in your coffee machines in line filter, if you have one in the water tank. This little inline filter becomes iron saturated a lot faster than the water softener resin beds (by revive, I don’t mean replacing the salts water solution purge you would do on a regular basis, this is purely to remove iron bound to the resin, this iron prevents ion exchange). If this paragraph is all gobbledygook to you, then best pay a professional, or keep buying those little in line filters.


RO Units also need a little maintenance once per year

To keep the system working well it’s advisable to disinfect the system on an annual basis. Again this is fairly easy and in the case of my system:

  • Keep about 6 litres or more of RO water, some to store the membrane in, the rest for flushing.
  • Remove all the filters, including the RO membrane and store the membrane in clean RO water
  • Bung in a few water purification tablets (from when my kids were babies), into the filter chambers, because no filters should be in the unit this is best done at one of the 12 monthly filter change, where all filters are changed (there are 3 filters on my system that have a 6 monthly change interval).
  • Allow the system to fill with water as usual, including the storage tank, give the tank a good shake, to fully coat the inside….wait a few hours. After this I drain as much water as I can from the tank, remove the filter housings and clean them all with the RO water I saved earlier.
  • Refit all the filters (including RO membrane), except the carbon post filter (you don’t want to contaminate it)
  • Switch storage tank tap off, and open RO water tap (the one you normally use for drinking water) to get water directly from the filter system and RO membrane, allow this to run for 15 minutes. Switch storage tank back on.
  • Drain water storage tank via RO water tap
  • Allow system to refill then, shake water storage tank (to get any solution at top of tank) drain tank via water tap, keep repeating until the water has no trace of the disinfectant solution (Milton or similar). This may take around 3-6 flush throughs (then refit carbon post filter).


RO water can be used in coffee machines with little problems and are best used in conjunction with household water softeners (The ro system works better) and you get the benefit of a scale free mix of water for your coffee machine. Mixing of the two types of water RO and Non RO can maintain the TDS at a level where espresso taste should be unaffected. Your coffee machine will last a lot longer and give a lot less trouble, in my case descaling is no longer necessary.

On the downside, these systems do have to be purchased, but a pumped RO system is relatively inexpensive, especially compared to using Brita jug filters, which in hard water areas need to be changed on an almost weekly basis, to be even partly effective! There is a little more expense to plumb it in, unless you are a competent DIY person.

Lastly, if you have a plumbed machine….none of this is any use to you and i would advise one of the calcium removal cartridges on the market, these are moderately expensive and have to be exchanged at regular intervals. If you don't do this though, you will quickly ruin an expensive espresso machine in a hard water area. Sure you could run a plumbed machine on a water softener, but there are pros and cons to doing this and in a commercial environment, I don't believe it is legal to do this.

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