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RO Water Purification: How it works

RO Water Purification: How it works


When we talk about pure water window cleaning or RO water we are referring to the process we use to filter normal tap water into pure H2O, ready to be used for your window cleaning. Many people think that when they see window cleaners using the extendable carbon poles to wash windows that they are just using standard tap water, and therefore can’t see why they couldn’t do their own windows with a long pole and a hose. There is nothing wrong with giving them a wash like this but this is not what we do at PPC, as all our water is purified through a series of 5 filters to produce pure water, or RO water.

Using pure H20 for window cleaning allows the dirt to effectively stick to the pure water and then just simply run of the window with a good rinse afterwards. This science happens as water in its purest form absorbs pretty much anything it comes in contact with which is why our tap water has been found to contain over 300 different manmade chemicals along with various organic matter and bacteria. When this water is applied to your window the dirt, dust and other particles will simply be sucked up by the water when brushed over the glass and then just run down the window when the operator rinses it all of afterwards. This water in its pure form cannot be consumed as it will dry your mouth out when it absorbs all of the bacteria found in your mouth. To give you an example of what is found in standard tap water have you ever seen a where there has been a leak from a pipe? You will normally see where it has been as there is a build-up of lime scale left which is just one of the standard things found in tap water, but never in pure water as this is removed at the first stage.

Depending on whether you live in a hard or soft water area you will probably find that your water is between 275 to 375 (PPM) which stands for Parts Per Million and it the total amount of dissolved solids in the water, which when purified is 0.00.

All of this magic happens in our filling stations with normal tap water being pressurised to 100 psi and then pumped through the following series of filters to produce 100% pure laboratory grade water:

1st Stage – Water softening

After the water has been boosted up to 100psi it passes through the very first stage which is a ion- exchange vessel to soften the hard water and make it easier to pass through the next 4 stages of filtration. This first process is to help protect the main RO membrane by removing elements like calcium, magnesium and other cations in the water which would usually cause lime scale. Once the water has passed through the softener its ready for the first stage in the filter process.


2nd Stage = Sediment filter

This is the first filter in the pure water stage with the water still being pumped at high pressure through the sediment cartridge to remove any suspended solids. This acts like a very tight sieve to remove micro particles that are found in our tap water up to 1/300 of the size of a human hair. Anything smaller than 1 micron will get through and reach the next stage of the process.


2nd Stage  = Carbon/ Charcoal Filter

The next stage of the process before the water even reaches the RO membrane is the carbon filter or charcoal filter. The water once passed through stage 1 enters a second pre filter which removes microscopic sediment under 1 micron, chlorine, fluoride, bacteria and other organic compounds found in unprocessed water. This works via a process called adsorption which is where the pollutants are trapped inside the pore structure of the carbon substrate, the same process as found in respirator masks or gas masks but with air passing through instead of water. Just one pound of activated carbon is the equivalent to surface area of 0.15 of a square mile or 100 acres, so very absorbent.


3rd Stage = Semipermiable membrane or RO filter

This is the most important stage of the water purification process as this is where the water entering the filter is still around 210 parts per million, and when it come out as pure water it is around 25 parts per million or (PPM) for short. The RO filter is a semipermeable membrane nearly 1 meter long that allows pressurised pure water to pass through it and be collected from one outlet, while it captures any impurities left from the first few stages in the second outlet, ready to be discarded as waste. The RO filter is the most important element in the production of pure water with many companies choosing to have this fitted in there vans which allows them to plug a hose pipe in and just fill up their onboard water tank. This is a long and slow process as it relies on mains pressure which can take up to 10 hours to fill 750 litres of pure water, considerably limiting the time an operator can work for before he needs to fill up again. PPC have several water storage facilities across the South storing up to 8000 litres of pure water at any one time. We also use high pressure pumps to allow operators to fill 1000 litres of our water in under 15 mins, which allows us to fill up and return to site several times a day if required.


4th Stage – Water Polishing


Once the water has been passed through the softener and three stages of filtration it is nearly pure and ready to use. At this stage it is around 20-30 PPM and just needs 1 more process to make it 100% pure, this stage is called polishing. The water is passed through a 11 Litre DI Vessel containing a resin which will remove any last and final impurities in the water and take it down to 0.00 before transferring it into our sealed holding tanks, ready to be used to clean your home or business.


The cleaning process


When our operators arrives at your home or business they will be usually carrying a large amount of this pure water in their on-board holding tank in there van. This is then pumped from the back of the van through another on board DI polishing vessel along the hose and up to the head of the pole that the operator is using to clean the windows. It is standard practice for any of the PPC operators to also clean your window frames too, as this will prevent any of the dirt build up on them making its way back onto your clean windows next time it rains. This is standard practice which helps to keep you windows cleaner for longer and improve the look of your home or business in general.

Here’s a run through of the stages at of our water units

If you would like to know any more about any of the processes we use then please get in touch with PPC Matt, as we are more than happy to answer any questions you may have.

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