Supply and treatment

In our district we are fortunate to have access to very high quality water sources to utilise as our public drinking water supply. However, treatment is still required to ensure the water we provide into homes and businesses is safe for those using it. Within the district the majority of our water sources are treated through a combination of Ultraviolet (UV) disinfection and chlorination. Providing multiple treatment barriers is necessary to ensure the safety of our water.  In a small number of schemes additional treatment steps may also be included such as filtration and pH correction.

UV Disinfection
Disinfection with UV light is a simple and effective method of addressing any bacteria and/or protozoa that may be present in the raw water. The high frequency UV light waves disrupt the DNA of the organisms, rendering them harmless.  The effectiveness of UV treatment is a factor of the intensity of the light radiated, the clarity of the water (UV transmissivity & turbidity), as a result this method of treatment is ideal for high quality raw water sources. However, UV treatment alone does not provide a robust barrier against viruses.

Filtration
A small number of our treatment facilities incorporate filtration as an additional treatment barrier to supplement UV disinfection and chlorination. Filtration is a physical process which prevents the passage of solid particles (both organic and inorganic). In our treatment plants filtration is utilised as a primary treatment process upstream of UV disinfection which ensure the UV disinfection can be as effective as possible.

pH Correction
Some of our raw water sources have low pH levels. pH is deemed as an aesthetic determined under the New Zealand Drinking Water Standards, however, when the pH is too low the plumbosolvency of water increases which can cause issues with older private plumbing. To address low pH chemical additives are dosed into the water. Within the district we utilise either lime or soda ash for this purpose.

Chlorination
The addition of chlorine to the water provides a barrier against bacteria and viruses (not protozoa). Chlorine disinfection kills the pathogens by breaking chemical bonds in the molecule.  A unique advantage of chlorination is that it provides a residual treatment capability as the water passes through the reticulation to the end users. This is vital to help address the risks arising from potential contamination points in the network. The Water Services (New Zealand Drinking Water Standards) Regulations 2022 requires that there is a minimum residual at the end of the network. QLDC operates their treatment plants such that the applied dose at the treatment plant is as low as possible so as to ensure the minimum level is achieved whist maintaining an appropriate factor of safety.

Fluoridation
QLDC does not currently add fluoride to its water supplies.

Only around half of all New Zealanders receive fluoridated drinking water, and until now, it’s been up to local authorities (councils) to make decisions around fluoridating their water supplies. The
Director-General of Health now has the authority to decide if community drinking water supplies
should be fluoridated. 

• Community Water Fluoridation Factsheet
• Letter - Fluoridation Bill