I have come across the Pharmatap Fillmaster FMF-940 which is a pharmacy grade reverse osmosis filter system. I would like to install it in my kitchen but before I do, I need some questions answered:

  1. Does the system drain constantly or just when it is refilling the tank?

  2. If it is constant, is there any way to adjust the flow? (It is a fast drip and would waste a lot of water if it is constant.)

I have never had a reverse osmosis system before, but I have heard they are pretty good for removing bad stuff from drinking water.

  • 2
    they drain only while refilling, yes it does filter the bad stuff along with good stuff too. I mean minerals are also filtered and you get nothing but plain water.
    – Shathish
    Commented Sep 23, 2013 at 8:23
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    You know drinking RO water over a long duration is bad for your health? Right! Pure water does not mean is is pure essence. Like pure Alcohol is harmful so can be pure water. You should really use activated carbon filters. But if you trying to filter out hormones in water then RO + reintroduce minerals and salts is needed, not just pure RO!! Carbon will not remove hormones from water but it remove chlorine and heavy metals nut leaves minerals and salts in place- keeping the waters PH neutral and buffered. RO water is unbuffered and goes acidic very easily!
    – Piotr Kula
    Commented Sep 23, 2013 at 11:59
  • PS Pharmacy grade means it removes 99.99% of particles, bacteria and viruses from water. The benefits of this is only for pharmaceutical use so that tests can be carried out on uncompromised base liquids. This kind of water should not be used for drinking.
    – Piotr Kula
    Commented Sep 23, 2013 at 12:08
  • Our tap water kinda tastes like dirt- that is why I want a filter. I cook with the tap water, the food covers the taste. I did not know about the mineral problem though, I will check into re-mineralization.. Any suggestions? Commented Sep 24, 2013 at 1:23
  • 1
    Only a miniscule amount of minerals are introduced through drinking water. The minerals you need are in the food that you eat not just the water that you drink. Remember you are what you eat!!!!
    – user54493
    Commented May 27, 2016 at 6:58

1 Answer 1


RO systems push water under pressure through a semipermeable membrane to allow the good part of water through and the bad part to stay in the input side and be washed away. Typical systems will operate with an efficiency of 4:1 or 5:1 meaning that four or five gallons of water go into the unit to produce each one gallon of filtered water. The rest of the water washes through the unit and goes into the drain. (This ratio can be worst for many older units whilst there are some manufacturers now advertising RO units with much lower waste).

My experience with RO systems is that they work well at producing clean drinking water. The initial equipment cost can be quite high as compared to a typical cartridge water filter system. But once that initial cost is past you there can be a quite long operational period without additional regular maintenance costs - that is unless the RO installation uses some post carbon filters which do require some maintenance.

The storage/filter tank that is part of an RO system can have problems however and if that happens replacing that part of the system can be a substantial cost. They can develop problems with the membrane or bladder inside the tank. There can also be problems with bacteria contamination in an RO system if it is not used properly. The manufacturer should provide instructions for their unit so that it is installed properly and kept serviced if necessary.

There are some health considerations with RO units in that they remove more things from water than just harmful things. Many of the beneficial minerals in the water are also removed by these units and there are arguments out there that this can be harmful in the long run if all the water you drink comes from an RO unit. As a matter of fact some commercial bottled water companies that produce their water via industrial scale RO systems are known to re-mineralize the filtered water to bring back some of its taste and benefits.

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    Re mineralization is very important for RO water. If done like this then RO filters are really beneficial as they remove everything from water, including hormones in water, especially in cities with frequently recycled water. Without salts the water is unbuffered and cause serious damage to teeth just by drinking it often and increases risks of ulcers or frequent heartburn due to raised acidity in the stomach. Humans are not designed to drink pure water. we need those minerals and salts.
    – Piotr Kula
    Commented Sep 23, 2013 at 12:05
  • @ppumkin - Stomach acidity is caused by your body producing hydrochloric acid. Drinking RO water can't possibly have any meaningful affect on it.
    – Mark
    Commented Jan 8, 2017 at 17:38
  • Not on the acid. The water absorbs the acidity and passes through highly acidic. Where it shouldn't be.
    – Piotr Kula
    Commented Jan 8, 2017 at 17:46
  • As far as RO they do take the lead and just about everything else out, if you take a multi vitiman there will be no harmful affects. I think carbon filters after an RO system are a waste of $.
    – Ed Beal
    Commented Mar 16, 2018 at 14:53
  • This doesn’t answer the OP’s question. Commented Mar 2 at 1:17

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