Reverse Osmosis (RO) Water Purification

Reverse Osmosis (RO) Water Purification

by PPC Pete

Reverse Osmosis (or ‘RO’) is a process of filtering normal tap water into pure H2O, making it 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 RO (also known as ‘pure water’).

Using pure H20 for window cleaning allows the dirt to effectively stick to the pure water and then just simply run off the window with a good rinse afterwards. This 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 off 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, imagine a stain left by a leaking pipe. You will normally see where there has been a build-up of lime scale, which is just one of the standard things found in tap water, left over. However, you will not see this with pure water as lime scale is removed at the first stage of purification.

Depending on whether you live in a hard water or soft water area, you will probably find that your water is between 275 to 375ppm (Parts Per Million) and it is 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 stages of filters to produce 100% pure laboratory grade water.

Water Filtering Stages:

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 it’s ready for the first stage in the filtration process.

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.

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.

Semipermeable 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 210ppm, and when it comes out as pure water it is around 25ppm. The RO filter is a semipermeable membrane, nearly 1 metres 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 their 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 Window Cleaners have several water storage facilities across the South storing up to 5,000 litres of pure water at any one time. We also use high pressure pumps to allow operators to fill 1,000 litres of our water in under 15 mins, which allows us to fill up and return to sites several times a day if required.

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 arrive at your home or business they will be usually carrying a large amount of pure water in their on-board holding tank in the 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 will improve the look of your home or business in general.

Further Information on Cleaning

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