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Part 1: Understanding wastewater within natural and human systems

Communities have different reasons for looking at wastewater management. Sometimes people are worried about pollution in the local estuary or river, or loss of kaimoana, or possible public health problems. Or there may be population and development pressures that mean the current system simply won't cope with further growth.

Whatever the initial reason, your community will need to explore a number of general ideas before getting down to the detail of choosing a particular technology. It will have to take account of new thinking about wastewater systems, about new (and old) technologies that might avoid problems you are facing now, and about new (and older) ways of thinking about natural systems. You will have to think about a much wider range of effects than has been considered over the last hundred years.

This part begins by talking about the natural systems your wastewater system will have to operate within. This includes looking at the idea of the 'water web', the 'three waters', how natural ecosystems work, and the 'services' and assistance they provide to ensure the survival and health of your community. The impacts of wastewater on these 'ecosystem services' will be looked at, as well as the more traditional concern of public health. After this discussion of natural and human systems, and the place of waste and wastewater management within them, we will take a brief introductory look at the general technical range of wastewater systems, which are covered in detail in Part Three.

At first glance this might seem like the wrong order. Surely it would be better to look first at the kind of technical wastewater systems available and their costs and benefits in terms of managing health risks? How they can be managed to reduce impacts on the environment could be considered later.

These issues of health and cost are extremely important. Preventing health problems is the main reason communities have provided a wastewater system in the past. However, this handbook offers a different way in to thinking about choosing a wastewater management system. Any system must, of course, protect public health, but there is increasing recognition that a wastewater system must be designed as part of the surrounding natural systems. It is now not a matter of 'throwing away' waste – even treated waste – into an environment which is somehow separate from your community. The issue is more one of designing a wastewater system that works within the natural systems that support the clean water, swimming areas, estuaries and rivers, and soils that everyone in your community uses and enjoys.

Ultimately this kind of approach will also reduce health risks from damaged soils, water supplies and ecosystems. Focusing on natural and human systems and understanding the biophysical characteristics of your area will help your community to choose systems that best deal with more immediate public health problems. For example, knowing your local soils and water table and their capacity to absorb and naturally purify wastewater will help you choose between wastewater systems.

Rather than overloading the natural processes that purify water and maintain soils, your wastewater system should be designed to work with rather than against these processes. Increasingly, both people's concerns and legislation require that a community think about the survival of natural processes as well as obvious environmental effects (see Appendix 2 for legislation relating to wastewater management). Understanding these processes before launching into the business of technical systems is fundamental to your community process for choosing a wastewater management system.