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How To Make Pure Water For Window Cleaning

  1. Use reverse osmosis method to filter tap water

  2. Send filtered water through a DI resin vessel

  3. Test the deionized water with a TDS (total dissolved solids) meter. TDS should be less than 10

  4. Pump the completed water to the window to be cleaned.

How To Make Pure Water For Window Cleaning

How To Make Pure Water For Window Cleaning

How To Make Pure Water For Window Cleaning

How To Make Pure Water For Window Cleaning

How To Make Pure Water For Window Cleaning

Window Cleaning, Window Cleaner in Wombourne - SafeShine Windows

The quality of water used be window cleaners that use the water fed pole method is very important. Using low quality water could result in lots of 'spotting' on the glass. In this guide we will take an in-depth look into how window cleaners make pure water.

In this article we will explain

  • How to make pure water - everything you need to know including why we use pure water, the window cleaning water system, reverse osmosis window cleaning equipment, the impact of water pressure on making pure water and the impact of temperature when filtering pure water,

  • DI Resin vessel - all that you need to know including ro di filter replacement, how long does di resin last and how to replace the di vessel head.

  • How to use a tds meter including - what tds meter reading for window cleaning and a tds meter reading chart.


Even now, over ten years after the first window cleaners started using pure water for window cleaning, people still peer into the back of my van and say to me, "what do you put in that water?". Generally, not realizing that I am a bit of a purified water geek they regret asking, as I go into the fascinating facts that I have build up over the years.


If you are new to window cleaning with deionized water and pure water window cleaning systems, then read on...

First of all the water is filtered through several filters and membranes to create very clean water. This water is very similar to spring water. The water then passes through a deionizing vessel. The result is pure H2O. If the water was 100% pure and had a TDS (we will get to TDS in a bit) meter reading of zero, then they say that in theory that the water wouldn't even conduct electricity as there are no particles in the water for the electricity to arc through. (I haven't tried this and I don't recommend that you do either). They say that the window cleaning water purification system known as reverse osmosis was developed by NASSA so that could recycle the water and effectively drink their own wee (again, I haven't tried this and I don't recommend that you do either!) So making pure water for window cleaning is actually rocket science.


So when the window cleaner uses his water fed pole to brush the glass then rinse the window with this special water, all that is left on the glass is the pure water. This means that when the window dry the dry clear.


So, here is how to make pure water for window cleaning.




First you must decide where you are going to make and store the water. Some window cleaners choose to filter the pure water straight into their vehicle, others choose to filter the pure water into a storage container and then pump the water into their vehicle when they require it. Some even harvest rain water but that's a subject for another time. Today we will concentrate on the two methods mentioned above.

1) Filtering straight into your vehicle - This means that the filters that make the pure water are housed along with the DI Vessel in the vehicle its self.


- No space required for containers as the water goes straight from the tap into the vehicle.

- Can be filled up at any location that has a tap (as long as you are there long enough to filter the water)

- Can be ideal if you don't have a drain near to the tap for the waste water.



- May be more likely to freeze in the winter as the hose to the vehicle will be outside.

- Makes it difficult to use the vehicle whilst it is connected to the tap.

- More weight to carry in the vehicle (i.e the weight of the extra filters and di vessel).

- More space taken up in the vehicle.

- More water connections in the vehicle increasing the chance of a leak inside the vehicle.


2) Filtering the water into storage container and pumping into vehicle when required.



- Can be filtered in a location that is not susceptible to freezing.

- Lots of water can be made in advance and stored.

- Vehicle can be used whilst pure water is being made.

- Water can be made during the day whilst you are out window cleaning.

- Less weight in your vehicle. (i.e the weight of the extra filters and di vessell)

- Less space in your vehicle.



- Any leaks may be inside (garage, unit etc)

- You would need to return to get more water if you run out.

- You may not have a drain and tap in a location where you have space to store.

- need an additional sub pump

- need space to make the pure water.


How To Purify Water For Window Cleaning - Method

For this I will use the example of making the pure water in the garage at home, but most of the method is the same if you choose to make the pure water in you vehicle.


I set up the Window cleaning water filtering system as follow:

Reverse Osmosis | Pure Water Window Cleaning | Safeshine Window Cleaning

The water comes out of the tap and first goes into the filter unit. It is important that there is enough mains pressure to filter the water. If you have low mains pressure then you may be able to use a pump to assist. I have found though that trying to force the water through to quickly lowers the quality of the water.


You may like to take a TDS reading before and after the water is filtered but we will come onto TDS in a bit.


The water comes out of the filter unit and as you can see from the infographic above the water is split into good and bad water. The bad water goes down the drain whilst the good quality water goes to the DI vessel. Here the water is polished. There is no bad or dirty water outlet from here, the water moves straight onto the storage tank.

When the water is needed, it is pumped using a sub-pump into the vehicle.


So the better the quality of the raw ingredients, in this case, tap water the easier things are. You can’t really do anything about the quality of your tap water, it is what it is. But how do you know what the quality is anyway? Well, the answer is to use a TDS meter.

How to use a TDS meter.

A TDS meter measures the Total Dissolved Solids in water. It does this by measuring the electrical resistance between points.

There are two main types of TDS meter used in window cleaning. A handheld TDS Meter, or an inline TDS meter. Here we will look at both. I use the HM TDS meter.

Hand-Held - A hand help TDS meter is ideal if you need to dip test something like a water butt. You simply dip the meter into the water butt and read the LCD screen on the meter. If it is tricky to read the screen because the water level is too low, or if it is too dark then you can dip the meter into the water and press the hold button. When you take the meter out of the water, the reading will remain on the screen.

In-Line TDS Meter - This type of meter will give you a live reading on a separate display. It is best used to monitor in real-time, the quality of water passing through a hose or pipe. This can be ideal if you want to monitor the quality of the water leaving the filter unit before it enters the DI.

When filtering water I tend to read the TDS meter in a couple of places. First, its good to know what the quality of your own tap water is. This doesn’t often change very much. I live in the west midlands in the UK and my tap water is around 250 ppm (parts per million). I will provide a TDS meter reading chart for different regions later.

Next, I like to know the quality of the water as it leaves the filter unit. This reading changes particularly when the unit has been turned off for a short time. I tend to turn on the tap and monitor the quality of the water. My water starts off at about 50 ppm for the first three to five minutes and then drops to about 9 to 14ppm. if I put the pipe into the DI unit at 50ppm it can significantly reduce the life of the resin. So I wait for 5 minutes and take another reading. When it has dropped to 9 to 14 ppm i plug it into the DI (without turning it off).

Finally, I take a reading as the water leaves the DI unit.

You can also use your TDS metre to prove to people that it is OK cleaning windows in the rain (see video). 

Tds meter reading for window cleaning

Following a filter flush and DI resin change my water is at 0 ppm. After a couple of days, this rises to about 3ppm and stays at this level for about five weeks. Once the TDS meter reading goes up to 4 or five I flush my filters and change my DI resin straight away. If not I would find that the reading will rise to 10+ after another day and then 20+ after that. This TDS meter reading would be too high for window cleaning.


RO DI Filter Replacement

If your TDS meter reading is above 15ppm going into the DI vessel then you may need to change your RO filters. If your TDS meter reading is above 5 on the way out of the DI unit then you may need to change your DI resin.

Changing your RO filters is fairly straight forward as it is a simple process of removing one cartridge and replacing it with another. My suggestion would first be to flush your RO if it has the facility.

Changing your DI is a little bit more tricky. First I would advise wearing some waterproof gloves as the DI can dry out your skin and cause irritation. Remove the di vessel head. Empty the old DI out of the DI Vessel. To put new DI into the vessel, put in just a couple on inches first, then tap the filter cartridge on the ground (about twenty to thirty times) to ensure that the resin settles before adding another couple of inches. Repeat tapping and add more until the resin reaches the top of the container. Some vessels come with a bit of foam that sits on top of the resin. Make sure that the di resin vessel is completely full, then replace the di vessel head.

How long does DI resin last?

This is dependent on the quality of the water going into the Di resin vessel. One tip to make the DI resin last longer is to run off about five minutes of water before you let the water into the DI vessel once it has been standing unused for any amount of time. The reason for this is clear if you take a TDS reading when you first turn on the unit at the point where the water comes out of the RO and into the DI. You will see a reading of about five times what it should be. This falls every few seconds and reaches a good enough quality after several minutes. Waiting for this reading to be correct will prolong the life of the DI resin giving you a greater amount of time between DI changes.

The final step is to check the quality of the water in the storage container and then pump it to the vehicle using a sub-pump.

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