Direct Flow Reverse Osmosis Water Filter

Direct Flow Reverse Osmosis Water Filters – Tankless RO Systems

What is a Direct Flow Reverse Osmosis Water Filter?

Traditionally, a reverse osmosis water filter employs a  tank for the storage of the filtered water. This tank empties when the tap is in use and refills via the reverse osmosis filter when there is no demand on it. Such systems constitute the majority of RO filters in use in domestic settings, where they produce consistantly safe drinking water.

Direct flow reverse osmosis systems aka. tankless RO systems, as the name suggests, do away with the tank by having a direct flow of filtered water to the filter tap; they are able to do so due to a higher flow rate, providiing freshly purified water immediately upon demand.

The basic operating principals upon which these reverse osmosis filters work is the same whether they employ the use of a storage tank or supply direct, that is that the incoming water is forced by water pressure though  semi-permeable membranes which have a pore size of between 0.1 to 5000 nm, depending on the filter designation.

The main difference between the two types of RO filters apart from the tank, is that whilst in general the tanked system will normally only employ a single RO membrane, the Direct Flow RO systems may use 2, 3 or more to achieve the higher rate of flow necessary.

Direct flow reverse osmosis water filter system

Benefits & Drawbacks

In terms of the availablity of filtered water, the traditional tanked reverse osmosis filter is perfectly adequate for a small to medium household where it will give many years reliable service however, one of the great advantages of a direct flow system is in space saving, the absence of a tank allowing it to be sited in situations of limited space and therefore it is also ideal for some smaller homes where space is at a premium.

In a larger household or in a commercial setting such as a cafe or restauraunt where there is heavier demand a tanked system may not be adequate and the higher flow rate of the direct flow systems would be required.

So what are the disadvantages of the direct flow type reverse osmosis systems? Well, the most obvious would be the higher price tag. The main reason for this being the greater number of RO membranes used by such systems. This also translates in to higher maintenance costs when it comes to membrane replacement (although this may only be once in 3 years or so depending on the model)

 To Summarise

     – Advantages

  • Space saving. No tank needed
  • The filtered water is produced on demand and may taste a little fresher over water that is left for extended periods in a tank.
  • The higher flow rate means that the water is always there when needed and thre’s no worry about the tank emptying
  • Economical – filtered water is only produced when it is actually required.


  • Higher initial purchase price
  • Greater maintenance costs
  • Where the water supply is unreliable or intermittant a stored supply may be an advantage.


Which system is right for you will depend on where you stand with the issues described above. Generally, if space is not an issue and you have a small to medium sized household then a good quality standard type reverse osmosis system will probably be more than adequate. If however you want a RO filter system but lack the space or you are in a situation of high water demand then it may be well worth your while considering investing in a direct flow model, which investment will likely repay itself many times over.

Puriflow Filters are pleased to be able to supply the following high quality direct flow reverse osmosis systems:


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