Waiheke wastewater is treated and disposed on-site. There has been pressure towards reticulation, but the community has resisted this.
There are a number of different systems which can be used to treat wastewater to different levels. The treated wastewater is then applied to the land where the water and nutrients can be beneficially reused (remembering that Waiheke has a restricted water supply, due to the use of rainwater tanks for collection). Traditionally septic tanks were used and these are perfectly adequate under many conditions, achieving full treatment of the wastewater in combination with a drainage field (soakage field). They do suffer if undersized, or if too much greywater is introduced (e.g. from automatic washing machines), or if the drainage field is not well-located, designed and installed. Also the indiscriminate use of household chemicals can cause failures.
Due to some instances of poor perfomance, most new dwellings now need to install a secondary treatment system, which is typically an AWTS (see below). Secondary treatment effectively brings the treatment that would be achieved in the soil into the treatment system, so that dripline irrigation can be used and so that poor soils and high water tables are less of a problem and there is less risk of ground or surface water contamination. It is important to note that an AWTS still contains an initial septic tank, so the same problems as described for septic tanks can occur, leading to costly maintenance issues and under-performance.
Some other system designs are also available which do not contain a septic tank stage, or which use a more resilient process, often at higher cost unfortunately. However, capital expenditure can be dwarfed by maintenance costs when systems are poorly designed, specified, installed or operated, so they may represent a better option in the long run. Many of these systems use less power as well. In some cases (e.g. large sections) it is still possible to install a conventional septic tank and when designed properly, they are not an inferior system.
(information needs to be added here)
The following links are to an external site where there is some information about the system type and some user comments. It is encouraged to submit your own experiences with each system type:
Septic Tank[1]
Aerated Wastewater Treatment System (AWTS)[2]
Media filters/reactors[3]
Vermicomposting Units/Humus Ecology Filters[4]