It is imperative for water to be treated before usage for each application. The hardness of tap water generally ranges from 8° to 20° dH, often causing hardness sediment (scale). For this reason tap water must be softened with a water softener. For some applications partially softened water of 2° to 4 ° dH is needed, while other applications require total softening (softened water of > 0,1° dH).
There are numerous applications for which softened water in varied qualities is needed.
In this case the purpose is to reduce the total salinity (salt content). This process decreases conductivity and is expressed in µS/cm. For example, the average quality of tap water in The Netherlands ranges from 250 - 850 µS/cm.
For the variety of applications and equipment additional qualities are required:
- < 10 µS/cm
- < 4,3 µS/cm
- < 3 µS/cm
- < 1,1 µS/cm
- < 0,1 – 0,2 µS/cm
The lower the required conductivity, the more steps in treatment are necessary.
Demineralized water can be made in various ways. The most common occurrences are: softening/demineralization followed by one or two streets of RO (Reverse Osmosis), demineralization cartridge or an EDI (Electro Deionization). In some circumstances it is also necessary to decrease the bacterial count, apart from the control and extermination of Legionella.
For hemodialysis patients, who are likely to be dialyzed three times a week, special water treatment installations are required. This is essential for conductivity, bacterial count and endotoxins. Next to this the whole dialysis flow system can be disinfected with ozone of hot water.
The standard settings (demands) for the variety of equipment and applications are registered in various documents:
- Tap water (drinking water): Vewin guidelines, EU guidelines and WHO norm (World Health Organization)
- Pharmaceutical and dialysis applications (PW, HPW, WFI): European Pharmacopoei, USP and NFN guidelines
- Laboratories: NCCLS, CAP and CLSI
- Hospitals in general: RIVM R4101 and EN 285-92
- Remaining standards: ASTM, ISO and guidelines for steam boilers