Selection of RO unit

Water treatment is often very complex and reverse osmosis (RO) as part of the water treatment process is also a complicated matter.  Reverse osmosis is mostly used to eliminate salts from the water.  In this process all microorganisms and most other suspended and dissolved solids will be removed as well. Water that has passed through a reverse osmosis desalination system is safe to drink but an assessment of water system after the RO system should be made to eliminate any risk of contamination.

For a person without backgrund in the water business, selection of a RO watermaker is at best based on an analysis of only a few parameters, of which price is the parameter that usually carries most weight.  The price is the first step in establishing a sense of 'where do I get most value for my money'.  However, to establish a more balanced picture than the price  parameter presents you with, it can be a good idea to compare different watermakers on basis of a series of key technical parameters in addition to the price proposal you have received.

Initially, however, it is critical that the water source for the future water supply is identified.  If the source is e.g. a well with salty water, it is necessary to have the water analysed to determined if the water contains elevated levels of minerals that could make reverse osmosis problematic. When these aspects have been identified steps can taken to negotiate the issues, e.g. removal of minerals and/or dosing of anti scalant chemicals.  At the same time the salt content must be assessed.  In addition to the current salt content of the water it is important that possible variations in salt content over the year are identified.  The selection of RO unit must be based on the 'worst case scenario' in terms of salt content to prevent interruptions in water production.   

There are typcally RO units that can treat low to medium brackish water, RO units that can treat medium- to highly brackish water and then, the most sophisticated RO units, those that can process even sea water. The price level for the different types of machines is often proportional to the salt content in the water.  This has background in the fact that the pressure required to deal with increasing levels of salt also increases.  This implies that low levels of salt can be handled by relatively low pressures e.g. 20 bar. Such RO units are available at relatively low cost.  Removal of salt from medium to highly brackish water or even from sea water, however, requires progressively increasing pressures, i.e. pressures from 20 to  70 bar.  This challenge requires specialised equipment which makes highly brackish and sea water capable RO units more expensive.  So you will have to choose a RO unit that matches the salt content that you have in the raw water.  

In case the water source is sea water it can be assumed that there are minimal variations in the chemical quality over the year.  However, an analysis should determine any organic pollution which could disturb the RO process.  In case of pollution, steps can be taken to eliminate or greatly reduce pollutants in the water before it reaches the RO unit.

Your local dealer will be able to assit you through the selection process but it is advisable that you also take some time to get an idea of the unit that suits your water quality and  also suits your financial capacity and your other wishes, with a view to e.g.  operating expenses, quality of the product, automatic or non-automatic operation etc.  Energy recovery systems in RO units of relatively small capacity is uncommon which makes power consumption fairly high for such units in general.  You could collect brochures and prices so that you have the basis for a balanced comparison.

On basis of these fundamental considerations it is advisable that a comparison of different RO units is made on basis of a number of key parameters.  An example of such comparison is made in this page: 

Files/Billeder/Comparison of RO watermakers November 2011.pdf