Ministry of Health. 2007. Optimisation of Small Drinking-water Treatment Systems: Resources for the Drinking-water Assistance Programme. Wellington: Ministry of Health.
Published in September 2007 by the
Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN 978-0-478-19144-8 (print)
ISBN 978-0-478-19147-9 (online)
In December 2013, legislation changed the term ‘public health risk management plan’ to ‘water safety plan’. Any reference within the text to ‘public health risk management plan’ has been changed to reflect the new legislation. No other changes have been made to this document.
Figure 1: Schematic diagram of a treatment process 4
Figure 2: Process schematic diagram 6
Figure 3: Trend of turbidity over time 7
Figure 4: Common features of a river intake 13
Figure 5: Infiltration gallery 15
Figure 6: Typical bore 18
Figure 7: Contamination of spring water 21
Figure 8a: Disc filter 24
Figure 8b: Horizontal flow gravel media roughing filter 24
Figure 9a: Cartridge filter system 28
Figure 9b: Used cartridge filters 28
Figure 10a: Straining of particles 31
Figure 10b: Attachment of small particles 31
Figure 11: Rapid gravity filter 31
Figure 12: Pressure filter 31
Figure 13: Relationship between pH and the form that chlorine takes in water 36
Figure 14: UV disinfection system 39
Figure 15: Groundwater from a simple bore water system (Scenario 1) 45
Figure 16: Cartridge filter system (Scenario 2) 46
Figure 17: UV disinfection unit (Scenario 3) 47
This booklet provides information about the supply of safe drinking-water to small water supplies serving fewer than 5000 people.
The intent of optimisation is to achieve the most effective and efficient use of a water treatment plant – which includes getting the best out of each piece of equipment that is part of the supply as well as operating and managing the supply in a way that produces the best quality of water possible.
Part of optimisation is to look at each piece of equipment and make sure it is working as well as it can. But, in addition to this concern with the contribution of individual parts of the plant, it is important to focus on the overall performance of the plant. This is because the performance of each part of the plant depends on the performance of the parts that come before it. For example, the performance of the ultra violet (UV) disinfection unit in Figure 1 will depend on the turbidity level of the water leaving the cartridge filter. In turn, the performance of the cartridge filter will be dependent on the performance of the multimedia filter system. All parts of the system will perform better if they are run for long periods of time, or even continuously, rather than being stopped and started.
Water suppliers are encouraged to try optimising processes to improve performance, provided the consequences of the changes do not result in the delivery of poor quality water to the consumer.
There are also some less obvious aspects related to getting consistent operation out of a plant, ranging from planning for unusual events such as natural disasters, to simpler issues like coping with the operator being away. Another aspect that is often overlooked is the operator’s own knowledge. In some situations the operator can be ‘optimised’ with some extra training!
The emphasis of this document is on issues that affect the safety of the consumer rather than on protecting assets and minimising costs.