How does pure water work?

Tap water (city water) has a number different kinds of dissolved solids held in suspension in the water. When the water is purified these solids are removed: however, pure water wants to return to it’s naturally dirty state. Pure water attracts the dirt from the surface being cleaned like a magnet. It collects the dislodged dirt, becomes dirty water, and drags that dirt down to the ground with it. Once the pure water has taken all of the dirt away, pure water will be the only product left on the surface. It will dry clean and spot free.

What are the real world implications?

Pure water cleaning is great in principal, but there are several obstacles the cleaner will need to overcome to get great results.

The general issues are as follows:

• Getting the water to the glass - This is generally accomplished with a WaterFed system designed to:

1.) Either carry pure water or make pure water on demand 
2.) Then pump that water to a nozzle and brush.

Most pure water cleaning of building glass is done with an extendable pole that has a nozzle and brush attached to the end. Some pressure washing systems also use pure water to avoid spotting i.e. Car Dealerships.

• Cleaning off the dirt and grime – Agitating the dirt and grime on the surface insures that it is freed from the underlying surface.  This allows the pure water to grab onto it and pull it down to the ground.
  
  • Pure water by itself is crucial to the cleaning process; however, it will not release dirt stuck to a surface on it’s own.  Therefore, using a brush or device to agitate the dirt off the surface and into the water stream is crucial.
    
  • Often improper agitation will show up on glass as vertical stripping of the dirt on the window.  this means that the agitation removed some, but not all, of the dirt.
    
  
  
• Rinsing the glass after cleaning – When water is applied to glass it will either sheet off cleanly and leave a clear surface, or bead up and leave droplets.Depending on the type of glass, different rinsing techniques will be necessary:
  
  
  • Glass where water sheets off cleanly is called Hydrophilic and is easier to rinse. Start at the top and rinse side to side.  Rinse far enough down until the pure water sheet all the way down to the bottom of the glass.
    
  • Glass where the water beads up on the glass is known as Hydrophobic and is more difficult to rinse. Start at the top and insure that every area of the glass is hosed down by the pure water flow.  Go slowly and watch for water that is flowing in different directions on the glass surface.
    Hydrophobic glass requires much more attention to detail: Where is the water flow hitting the glass: Have you rinsed all of areas where the beaded up droplets are? A poor rinse technique on Hydrophobic glass will appear as water spotting, usually at the bottom of the glass, or in an Angels Wings pattern where the rinse water avoided a specific spot as it ran down the glass.

Note on Self-Cleaning glass:

Self Cleaning glass sold by Pilkington and PPG have a coating applied that turns the glass Hydrophilic. The dirt does not collect into droplets and therefore does not accumulate into spots. This glass needs water, generally exposed to the rain to actually be self cleaning, This means that Self Cleaning Glass installed in an alcove, under an awning or places with little rain will not self clean. This makes this glass easiest to clean with pure water.

Building cleaning uses small-scale water purification to create pure water. We say building cleaning because in most cases more than just the glass is cleaned when pure water is used. The window surroundings, adjacent building siding, exterior of gutters, and eaves can all be cleaned with pure water. Glass cleaning is the most demanding use of pure water for cleaning.

1. Pure water used for glass cleaning should be less than 10 parts per million (10ppm) TDS.
2. For Automobile and similar painted finishes the water should be less than 50ppm.
3. For other building surfaces the water should be less than 70ppm

The ppm figures above are the upper ranges for cleaning in order to avoid visible water spotting on the cleaned surfaces.

De-Ionizing (DI) resin

The most important part of creating pure water is the electrical exchange process where the dissolved solids are removed from the water. In small scale systems, De-Ionizing (DI) resin is used to perform this process. The DI resin process uses positively and negatively charged resin particles to attract and capture the many different kinds of dissolved solids suspended in the water. DI Resin is made up of two styles of resin, one is an Anion resin the other a Cation. DI resin is stored in one or more tanks or cartridges. Water is passed through the resin and the dissolved solids are attracted to the resin. The water that leaves the tanks is pure. Some systems use separate tanks for the anion and cation resins, others are Mixed Bed tanks with both types of resin combined in a single tank.

As the TDS in the water is removed, the DI resin will eventually become saturated and stop attracting the dissolved solids. Therefore, the pure water stream should be tested frequently to insure the DI resin is still performing as expected.

The total TDS in the water varies considerably across the country. It can even vary within a city depending upon the source the water is derived from (well water vs. river water) and the type of minerals and other solids are contained in the water. DI Resin prices have fallen over the years, yet they are still expensive enough that some tap water can not be cleaned by the DI Resin alone in a cost effective manner.

De-Ionization is the key to pure water cleaning. Electrically removing the dissolved solids turns the water into a safe, yet effective cleaning agent.

But in some cases, DI Resin alone can get expensive:

An example of the costs of creating pure water is shown in this chart for the 3Star DI Resin Cartridge system:

• 100ppm TDS (medium hard water) will cost about 12¢/gal. to clean
• 200ppm (hard water) about 24¢/gallon
• 400ppm (very hard water) about 48¢/gallon.

If we suppose that a the typical rate for cleaning glass is just less than a 1 gallon per minute, then a typical worker will consume 50 gallons an hour. Further, lets presume that the pure water is used for 6 hours a day, 20 days a month, and 12 months a year.



Lets also now figure that two houses per day are cleaned. We can then calculate the cost per house for the DI resin consumer. Each house would require: at 100pp - $18, at 200ppm - $36 or and at 400ppm - $72 in resin costs. $72 per house, when using DI Resin alone, is an expensive method of creating pure water.

So if the DI resin is the important component in pure water cleaning, then how can we extend the life of the product?

Multi-Stage filtering systems are the answer. These systems were developed to remove as much of the TDS prior to the DI resin electrical charge final polishing.

Multi-Stage filtering systems are generally made up of multiple filtering devices each designed to reduce the overall cost of creating of pure water and each contain at least:

1. A sediment filter to remove larger solids like sand and rust flakes.
2. A carbon filter to remove chlorine from the water supply and avoid damage to the RO Membrane.
3. A Reverse Osmosis (RO) membrane to remove 90 to 97% of the dissolved solids.

Multi-Stage filtration requires high pressure to perform well, often input water pressure is enough to get the job done; however, pumps are required when input water pressure is below 40 PSI. They are also recommended for pressure below 60psi. The higher up the surface, the more pumps come into use. With water at 80psi and a surface at 2 stories, it is possible to clean without a pump. Beyond that there are several factors to consider: the number of cleaning devices and at what height the surface to be cleaned is. The typical pump is a 110V, but a 12v form is also avaibable for jobs requiring lesser capacity. All of the equipment in the catalog has some basic rating for what it is capable of.

This filtration system can reduce the cost of the water per gallon to 10% or less of DI resin alone. The savings in DI resin cost can pay for the RO/DI filtration equipment in as little a one to three years - depending on the total TDS of the in coming tap water.