Love coffee, consider this counter top Reverse Osmosis system with a difference!

If you own an expensive coffee machine costing £100s or £1000s of pounds this unique Reverse Osmosis solution from Osmio Water is just what you need. I cover the merits of the system in keeping your coffee machine in great condition, with fewer faults and the positive impact on taste and convenience.

Designing and testing of many prosumer coffee machines, roasters and grinders for 15 years taught me that 90% of coffee machine problems are caused by poor quality water (not just limescale). With machines costing many thousands of pounds, faults and problems are something I want to avoid.

The videos are for evidence based reviewing and information, not polished sales presentations but I urge you to watch them. You can see what really happens and how it works in a real home and perhaps benefit from my experience. I asked to review the Osmio Zero because it looked very interesting and appeared to fulfil all my needs. Usually companies approach me for reviews and I’m quite selective. I have no affiliate links and I don’t get commission if you buy an Osmio Zero.

What is Reverse Osmosis (RO)

Wikipedia defines Reverse osmosis (RO) as a water purification technology that uses a semipermeable membrane to remove ions, molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure.

It’s OK if you glazed over before you got to the end of the paragraph above. My take on it is, a molecule of water is really tiny, the other rubbish in the water is larger. If we get a special filter with holes just big enough for the water to go through (the RO Membrane), and apply enough pressure (using a pump)…we can squeeze just the pure water through and leave almost all the other stuff behind. It’s a molecular sieve with really tiny holes, clever really.

There are myths surrounding RO water, suggesting your bones will crumble if you don’t get the minerals in the water, or it’s acidic and will affect your bodies acid balance and lots of other fallacies. None of it is true, it’s pure water with nothing added. Unsurprisingly filter manufacturers will say one thing RO manufacturers will say another and if they sell both, they will be on the fence. You can read Osmios take on it here

Why I chose Reverse Osmosis

15 years ago I realised water purification was necessary because my expensive coffee machines were scaling up and developing faults within 6 months to a year. Sometimes the faults were subtle, early indications of problems that would become much more expensive to fix if not dealt with immediately.

Tap water has things in it that I personally don’t want to drink, it’s not just about hard water. I don’t think it tastes or smells that great, can at times smell like river water and always has too much chlorine, none of this helps the taste of my coffee. Reverse Osmosis water, seemed a good solution and with correct treatment for acidity, could be made coffee machine safe and would taste great.

The issues around RO systems typically are, installation costs, space for the system, faults, sterility and waste water. I am a bit of an eco warrior, so the waste water bothers me a lot and I will cover these areas in the review. You may not be an eco warrior, it’s expensive, so what’s in it for you and why the Osmio Zero?

How does this help me, my coffee and my coffee machine

Reliability & Protecting your investment

Expensive coffee machines cost from £300 to £5000, faults and repairs are expensive. If you can’t do them yourself, properly boxing, insuring and transporting a 20+ kg espresso machine to a repairer is a risky, expensive hassle. Water that has a high level of hardness and/or other impurities is the main cause of espresso machine problems. In a hard water area, I can pretty much guarantee that you will have a water related coffee machine problem within 2 years. Descaling machines often causes problems with loosened lime scale clogging valves and solenoids, plus the internal corrosion such descaling causes.

Whilst the machine is clogging up with lime scale and other deposits, it’s operation is affected. Temperatures accuracy is affected, boiler fill levels change, group thermosyphon flows change, expansion valves and vacuum breakers begin to leak. All these things make an espresso coffee machine run far less well than the day it was new. If you have a Bean To cup Machine, these are equally badly affected and an expensive hassle to keep descaling. Once they go faulty, they usually end up in landfill.

Using RO water with a very low level of contaminants makes total sense.

Easy Installation, Convenience & Taste

If you start buying bottled water to try to preserve your machine you invariably use it for Tea and drinking water because it tastes better than tap water. Unfortunately it’s expensive, very bad for the environment and the inconvenience of buying, storing and transporting it each week.

Most people with expensive coffee machines end up using bottled water (some only learn after a few expensive repairs), it’s better than tap water, but can vary in quality/formulation. Generally only the more expensive ones are relatively “coffee machine safe” and you do have to carefully check the mineral content. By relatively I mean that eventually you are going to need to clean things or descale. Some move on to RO systems, or would if the systems didn’t need to be plumbed in, require maintenance and use a whole kitchen cupboard.

The Osmio Zero is simply unboxed, placed on the counter and plugged in. No waste, no plumbing no pipes and no hassle. It can be up and running within 10 minutes of receiving it. You get clean, great tasting RO water that’s machine safe, using tap water you already have in your home. It’s also an instant water heater, heating only the water you use, when you use it, saving energy and helping the environment. This means you don’t really need a kettle.

The following assumes 2 litres of fluids per day per person : Volvic is good water for coffee machines and coffee/Tea making. If you were single you could easily be spending £300+ per year and for a family of 4 this quickly rises to £1200. Even the cheapest water that isn’t too bad for coffee machines (Tesco Ashbeck) costs over £160 per year for 1 person or £640 for a family of 4 and that’s buying it in 5 litre containers!

My reasons for changing to a counter top RO system

I have used under counter Reverse osmosis (RO) systems for 15 years, the first, a 5 stage non pumped system, slow and very wasteful of water. I moved to pumped systems, faster and more efficient, but they still waste a lot of water and am currently on my 5th system. Two of them were changed because on one the pump failed, on the other the waste water valve failed and it continually discharged waste water into the drain 20 hours per day for 4 months before I realised. I am on a water meter and the fault cost me an extra £300 on my water bill! The others were changed out for end of life reasons. I should add that I have not included the water for flushing the membrane, the under counter system automatically does that periodically to try to maintain membrane performance.

I initially looked for counter top systems 15 years ago and every few years since, but none were suitable. At best, they needed to be beside a sink with a plumbed waste, or rubber pipe, or they had to be fully plumbed. They were bulky, slow and not particularly user-friendly. So I had to choose an under the counter plumbed in system with a tank that filled an entire kitchen cupboard. They need maintenance as well, but it’s such a hassle even I don’t do all the maintenance I should. There were 4 key reasons I wanted to change to a counter top system exactly like the Osmio Zero.

1. Maintenance and sterilisation

Under counter systems usually have a tank and 5+ filters to be changed every 6 months, some less often depending on type (RO membrane). RO systems typically become contaminated over time and require sterilisation. Inside the all filter holders you can get moulds and slime. Algae can grow inside the RO storage tank. Pumps break, solenoid valves can fail and leaks develop . Over 15 years I had all these problems and would usually replace the entire system every 3 or 4 years. The filter housings should be sterilised at least annually and personally I think 6 monthly would be good. It’s a complicated procedure and each time you open and close filter housings there is the possibility of leaking and sterilising the water storage tank (to avoid algae) is a major hassle and should be done 6 monthly. I only realised they needed sterilisation after taking apart my first system and seeing what was hidden inside various components, it wasn’t pretty.

The Osmio Zero has the all in one filter cartridges changed out every 6 months (including the RO membrane) so it remains clean and efficient. Filter changes take only a few minutes and no big sterilisation hassles

2. Faults, leaks and Installation hassles

An under counter system attached to the mains water supply may leak and that can be a lot of water. If the electronic valve goes faulty to the waste, as mine did on one of my systems, it’s a huge amount of water down the drain and it took 3 or 4 months for me to notice and cost me well over £300 extra in metered water charges!

The Osmio Zero only has a 5 litre tank and faults don’t result in a kitchen flooded with water, an insurance nightmare, especially if they ask who installed it. Or hundreds of pounds of expensive water going down the drain if a solenoid valve fails. At worst a fault results in 5 litres of water on the floor. The little Osmio can easily be maintained or fixed (I asked if parts were available) without working inside a kitchen cupboard and having to turn the water off. 

Installation hassles. Ideally under counter systems should be installed by a plumber unless you are quite handy. When I installed my first RO system, I was stupid enough to use a self piercing clamp valve on the pipe and it’s always worried me it will leak. It has the additional disadvantage of weeping water even when closed, so to maintain my system I have to shut the house water off!

The Osmio Zero takes less than 5 minutes to install. You get it out of the box, wash the tank, fill with water and plug it in. No plumber or plumbing knowledge required. It has the filters in place all ready to go. Note: This doesn’t include the time taken to discard the first 5 litres of water

3. The amount of waste from conventional systems.

It’s a lot and I never felt comfortable about that. The Osmio Zero might seem expensive, but not when you consider the true comparisons over 5 years. If you have metered water, significant waste of potable drinking water is expensive and environmentally bad. I believe in evidence based reviewing, so a short video to make clear what’s happening.

A little man maths about the waste. My under counter system produces 4 litres of RO water for every 20 litres (or more) wasted. This waste water, which is clean tap water simply goes down the drain. The Osmio Zero produces 4 litres of RO water for every 1 litre of waste, that’s 20 times less waste. I calculated the surprising waste water cost from my under counter RO system based on around 12-16 litres of RO water we use as a family every day, it’s almost £80 of per year because we are on a water meter!

Even if we don’t worry about the cost, it’s not right to send almost 22,000 litres of good drinking water straight down the drain every year!

In comparison, the little Osmio Zero, only produces around £4-6 of wasted water in a year and even this water can be used for cooking vegetables, pasta, washing up, watering plants or cleaning recycling, so it’s not really wasted! The savings in water (if you’re on a water meter) more than cover the cost of new filter cartridges every 6 months.

If you are on a water meter, the whole life cost of the Osmio Zero is cost neutral or better when compared with an under counter system. It doesn’t cost more for convenience, or to be green.

4. Other Risks

I have other concerns that may be groundless, but I have them anyway. I suppose they are my own personal water phobias

A change in water quality when they work on the water pipes and the first you know of it is when you turn on the tap and brown water comes out. This can be soil contamination. If your RO system has been filling, you won’t see this and it has serious consequences for contaminating your RO system. The best case is that you will have to replace all the filters before the RO membrane, the worst case is that all filters and the membrane will have to be replaced and the entire system sterilised. Remember RO systems are only meant for potable water.

With the Osmio Zero, this isn’t such a concern, because you always see the water in the tank before you place it in the machine and can prevent any problems.

I guess this phobia applies to any RO system. When there is a notice to stop drinking the water because tests have shown a problem. I would immediately wonder when they found out and how long this has been going on for. Sure RO systems are only meant for water that is potable (safe to drink) but I still feel happier that I have been drinking from an RO system and not the tap in the event of a problem like this. I guess I am just not that trusting a person about overall water quality and whether we are actually told everything in a timely fashion. However, I do believe tap water is safe to drink (unless the water company tell us otherwise) because it’s loaded with chlorine to keep it sterile.

Coffee Machines and RO (slight tech warning)

This is a subject I have researched for 15 years. RO water becomes slightly acidic for a couple of reasons, CO2 will diffuse across the membrane and removal of all the Calcium and Magnesium carbonate (dissolved limescale) removes their buffering effect to an increase in acidity. CO2 on the air can now more easily dissolve in the water and form a little H2CO3 or carbonic acid. No dissolved limescale means that relatively small amounts of this acid raises the pH more than you would think. The pH can go down to around 6.5 or 6.4, about as acidic as milk. It is unlikely to do any harm in the short term to a coffee machine, but I suppose there “might” be a small risk over decades…remember milk isn’t very acidic (think about when you last drank it). Fortunately this can be easily fixed by adding 0.1g of sodium bicarbonate to every litre of water. When shopping for it in the supermarket don’t buy baking powder, it’s not the same thing. It’s the amount I found during experiments over the years that delivered a number of benefits:

  • Keeps the water pH neutral or slightly alkaline, exactly what we want
  • You can’t taste it at all in these quantities and it’s not harmful
  • It raises TDS to around 80-120 considered a good level for making espresso,
  • Non scaling despite the TDS reading, but machine protective
  • Allows the taste buds to function as they do in hard water by not having a zero ionic concentration.
  • The coffee tastes good and extracts correctly

On the last point I would say that I have actually not had a problem with taste or extraction using pure RO water, but some people say they do. RO is a no brainer when it comes to expensive coffee machines. Pour over/brewed coffee also benefits and speciality tea which my wife is into. For the latter RO water with no treatment or just the Osmio light remineralisation cartridge is absolutely perfect.

The Osmio light remineralisation cartridge comes with the machine and is the 4th small square installed filter with the ring-pull on it. It contains ceramic calcium and magnesium. I also have a blank one with nothing in it, allowing me to choose, or not choose remineralisation. The introduced levels of calcium and magnesium are around 30-50 TDS. The variation is mainly because of the ever increasing osmotic concentration in the supply pitcher. So if you draw water to refill your espresso machine tank, realistically you will be at the 30-40 TDS mark for these minerals. I believe at these levels you won’t see machine problems due to scaling or actually need to descale often (perhaps every 10 years) if at all. So far tests with this cartridge have it keeping pH under reasonable control, so an alternate water treatment plan for coffee machines could be 0.08g of Bicarb per litre and leave the remineralisation cartridge in. I’m still testing this area and will update soon.

Is it perfect can anything be improved?

I suppose nothing perfect but it’s pretty good and I believe better than other counter top systems I researched to replace my under counter system. The areas I think perhaps could be developed further:

  • Slidey foot fitting rather than only the grippy rubber option. The rubber feet don’t take a stick on furniture pad well.
  • Productised sterilisation system and blank filters for the obsessives (coming soon)
  • Programmable amounts for water and hot water
  • Blank finishing cartridge for those who don’t want to add minerals back (coming soon)
  • Stronger magnet on drip tray and rubber foot dots for drip tray so it grips counter (can be mitigated by purchase of small disk magnet and rubber dots from shops)
  • Perhaps a LED to illuminate the cup area when drawing water or when machine wakes up
  • Simple system for increasing the low water limit for filling up main tank, allowing users to increase membrane life in very hard water areas.
  • The instructions state 5 litres to flush, my wife and I could still taste the antibac compounds they put in the filters and other tastes associated with a new system for about 12-15 litres. It was OK after 5 litres, but perfect after 15 litres.
  • I’d like to see parts listed on the Osmio website soon.
  • Perhaps more creative filter deals if possible, making this system accessible to more people even if they don’t have a water meter.

That’s about all I can think of and some might increase the price of the product which I wouldn’t want to see, especially as a lot of it can be done by the customer. It is close to perfect, if I was designing something like this, I would be hard pushed to do a better job than Mark has, and he clearly knows his stuff where RO is concerned. Below another video giving my thoughts after weeks of use.

Who should buy this system?

  • You want to drink RO water and use it for Tea and Coffee, then consider this. It’s simple, easy and tastes great, you can be up and running in minutes with no installation.
  • You own an espresso machine, consider this, especially if you have a small kitchen as you can potentially save a lot of space vs a conventional system and definitely be space neutral when comparing it with a large container of water and a Kettle.
  • Those in rented accommodation or are often on the move or have a very small flat or kitchen.
  • If you have a whole house water softener, these systems work even better with softened water. If you have a water softener like me, your water will be really hard. The good news is the membrane should last as long as in a lower hardness area and filter faster. It’s also means you are not drinking the softened water direct, but only after removal of any salts.


I’ve been using the system for over 2 weeks now and I have to say I really like it, a lot. It’s saved me time and space both above and below the counter. It makes life so much easier and everyone in the family loves it. On the cost front, sure there is a larger outlay initially, but doing the math it actually works out cost neutral (family of 4). Based on being on a water meter and the fact that under counter systems need end of life replacement and filters over time. I truly believe it doesn’t actually cost more to be greener and you get a heap of convenience thrown in.

If you are not on a water meter then sure it’s going to cost more than an under counter system but if you can afford it…why not save all that clean water from going down the drain. For bottled water users, it’s going to save a lot of money and definitely help the environment in terms of plastic waste and the carbon used to produce and transport the water to the supermarket, only for you to transport it again.

I’m doing some additional small articles just to help coffee machine users and also a sheet and video on how to sterilise the system over the next few weeks. These are just things that I need more time to set up…

If you can afford an expensive coffee machine, then you really need to use great water and the little Osmio Zero gives great water!