De-Ionised (DI) water is used to produce spot free cleaning without the use of chemicals, detergents etc, the use of DI water was forced on the window cleaning industry when a European directive was issued which banned the use of ladders that were not fixed at the top, which made traditional window cleaning impossible.
In window cleaning the water is produced from mains water via sediment and carbon cartridges and then through an RO membrane and DI to storage, from there it is pumped via a long reach pole system.
Most window cleaning systems are mobile, including the water treatment, and are fitted within a van. Some companies have larger pure water production systems and fill more than one van from this central system.
In some very rare situations where the mains water is very soft the storage tank will hold mains water and this is then pumped to the long reach pole via a DI vessel.
The other applications involving washing glass including glass / crystal manufacturing and sealed window units production, produce the water by the same process and then spray it onto the finished product as the final stage of cleaning.
Automatic car, truck and bus washing systems use Filtration and Water Treatment methods to produce RO quality water to create a spot free final result. These systems can sometimes also recycle the used water by catching in a sump, treating and re-using.
A similar principle to the applications above whereby industrial catering firms use RO quality water for the final rinsing of the dishes and glasses, again to generate a spot free final result.