Production & purification of drinking-water as per WHO
The specifications for WPU found in compendia (e.g. pharmacopoeias) do not define the permissible water purification methods apart from for BWFI.
The chosen water purification method or sequence of purification steps must be appropriate to the application in question. The following should be considered when selecting the water treatment method:
- The Final water quality specification
- The quantity of water required by the user
- The available feed-water quality and the variation over time (seasonal changes)
- The availability of suitable support facilities for system connection (raw water, electricity, heating steam, chilled water, compressed air, sewage system, exhaust air
- The sanitization strategy
- The availability of water-treatment equipment on the market
- The reliability and robustness of the water-treatment equipment in operation.
- The yield or efficiency of the purification system
- The ability to adequately support and maintain the water purification equipment. the continuity of operational usage considering hours/days, days/years and planned downtime.
- The total life-cycle costs (capital and operational including maintenance).
The specifications for water purification equipment, storage and distribution systems should take into account the following:
- The location of the plant room
- extremes in temperature that the system will encounter
- The risk of contamination from leachates from contact materials
- The adverse impact of adsorptive contact materials
- Hygienic or sanitary design, where required
- Corrosion resistance
- Freedom from leakage
- A system configuration to avoid proliferation of microbiological organisms
- Tolerance to cleaning and sanitizing agents (thermal and/or chemical)
- The sanitization strategy
- The system capacity and output requirements
- The provision of all necessary instruments, test and sampling points to allow all the relevant critical quality parameters of the complete system to be monitored.
The design, configuration and layout of the water purification equipment, storage and distribution systems should also take into account the following physical considerations:
- Ability to collect samples
- The space available for the installation
- Structural loadings on buildings
- The provision of adequate access for maintenance
- The ability to safely handle regeneration and sanitization chemicals.
Production of drinking-water
Drinking-water is derived from a raw water source such as a well, river or reservoir. there are no prescribed methods for the treatment of raw water to produce drinking-water from a specific raw water source.
Typical processes employed at a user plant or by a water supply authority include:
- Disinfection or sanitization (e.g. by sodium hypochlorite (chlorine) injection)
- Iron (ferrous) removal
- Reduction of concentration of specific inorganic and/or organic materials.
The drinking-water quality should be monitored routinely to account for environmental, seasonal or supply changes which have an impact on the source water quality.
Additional testing should be considered if there is any change in the raw water source, treatment techniques or system configuration.
Trend review may be used to identify changes. If the drinking-water quality changes significantly, but is still within specification, the direct use of this water as a WPU, or as the feed-water to downstream treatment stages, should be
reviewed and the result of the review documented.
Where drinking-water is derived from an “in-house” system for the treatment of raw water, the water-treatment steps used and the system configuration should be documented. Changes to the system or to its operation
should not be made until a review has been completed and the change approved by the QA department in accordance with change control procedures.
Where drinking-water is stored and distributed by the user, the storage systems must not allow degradation of the water quality before use. After any such storage, testing should be carried out routinely in accordance with a defined
method. Where water is stored, the system design and operation should ensure a turnover or recirculation of the stored water sufficient to prevent stagnation.
The drinking-water system is usually considered to be an “indirect impact system” and does not need to be qualified.
Drinking-water purchased in bulk and transported to the user by tanker has additional problems and risks not associated with drinking-water delivered by pipeline. Vendor assessment and authorized certification activities, including confirmation of the acceptability of the delivery vehicle, should be undertaken in a similar way to that used for any other starting material.
Equipment and systems used to produce drinking-water should be able to be drained and sanitized. Storage tanks should be closed with appropriately protected vents, and should allow for visual inspection and for being drained and sanitized.
Distribution pipework should be able to be drained or $ushed and sanitized.
Special care should be taken to control microbiological contamination of sand “liters, carbon beds and water softeners. Once microorganisms have infected a system, the contamination can rapidly form biofilms and spread
throughout the system. Techniques for controlling contamination such as back-flushing, chemical and/or thermal sanitization and frequent regeneration should be considered as appropriate.