We all want to improve the quality of our waterways and we need to work out the best way to do this. We might get better outcomes by reducing contaminants in stormwater, rather than spending a lot of money reducing wastewater overflows. For example, to eliminate wastewater overflows altogether would require converting most of the city to a pressure sewer system and would cost more than $3 billion to build. However, it would not necessarily result in an improvement in water quality.
The Council carries out extensive monitoring of the water quality in our waterways and in the past year has collected and analysed over 7,000 water quality samples.
The key contaminants were:
- Sediment – the main contributor for poor water quality, which smothers habitat and food and can be contaminated. This comes from runoff from construction sites, unstabilised surfaces, vehicles and earthquakes.
- Metals (zinc and copper) – toxic to fish and other creatures. These come mainly from brake pads, tyres and building products (roofs, spouting and down pipes).
- Bacteria – create a public health risk. Bacteria mostly come from ducks and dogs and occasionally from wastewater overflows.
- Nutrients (nitrogen and phosphorus) – can be toxic (e.g. ammonia) and can encourage the growth of weeds and algae. Nutrients come from fertiliser, soils, and the faeces of livestock, dogs and ducks.
Most water quality monitoring sites show remained steady since 2007, with some sites worsening and some improving. Following the removal of large amounts of sediment, the waterways have been returned to prequake environments. The Council prepares a water quality monitoring report every year.