New threats are entering our cities' waterways, adding to the long-known problems of microbes, human bugs and heavy metals.
Scientists are discovering a new range of potential pollutants like pharmaceuticals and personal care products, such as toilet soap, shampoo and shaving cream, which can release potentially harmful substances into urban streams and beaches.
Freshwater ecologist Dr Kevin Simon, of the University of Auckland, says water quality problems in cities include things we've known about for a long time – "microbes, human pathogens and heavy metals that run off into streams."
But scientists are starting to look at new potential pollutants: "That includes things like pharmaceuticals and personal care products (PPCPs). Recently we've also started looking at plastic pollution in urban streams. There's a wide diversity of things emerging, some we know a lot about and some we don't know too much about."
University research from the US revealed late last year that human antidepressant medications were accumulating in the brains of fish in the Great Lakes region, with earlier research suggesting the effects could be making fish unusually aggressive.
"The continuous release of PPCPs into freshwater systems impacts the health of aquatic organisms," the researchers from the State University of New York concluded, adding that the cause was "direct exposure" to the discharge from wastewater treatment plants.
Approximately 70 per cent of consumed pharmaceuticals in the US are excreted in urine, and subsequently aren't filtered out by most municipal sewage systems, meaning medications and chemicals from personal care products end up in waterways there.
The phenomenon is still being researched and is new enough that there are few theories on what can be done.
There are other, older causes of pollution we can address. It's well known that copper and other heavy metals like mercury, lead, cadmium and chromium are present in most of the brake pads of New Zealand cars.
According to Environment Canterbury, copper from brake pads is the most common metal pollutant in waterways – and can have lethal impacts on urban water quality and aquatic life: "When we use the brakes on our car, fine particles of copper and other metals within the pads flake off... When it rains, these particles are then washed into the gutters and through the stormwater system where they flow into our rivers and lakes."
A solution? Environment Canterbury say low copper and copper-free friction materials are only $10-$15 more expensive than traditional pads and do not compromise safety or performance.
Simon, who specialises in human influence on lakes and streams, says New Zealand is not unique: "What we see in New Zealand is symptomatic of urban systems everywhere. A lot of the problems in urban streams have to do with how we use water. All the impervious surfaces we put down on the catchments lead to rapid run-off that can move pollutants into the streams.
So what can the average person do?
"Keep in mind that a lot of what you send down your drains can often make its way into streams, especially in the older parts of Auckland where the stormwater systems and the sewerage systems are not separate. During heavy rainfall, those older systems will discharge directly into streams. The newer parts of the system have sanitary sewers that always keep the sewage going to the water treatment plants."
The answer is water-sensitive design that mitigates run-off.
"Some people will put in rainwater collection systems so they can hold water and use it as grey water, or reduce the use of chemicals like fertiliser and pesticides when working on lawns and gardens.
"Things like green roofs that minimise our water use and minimise letting water run off the land quickly into streams are pretty important."
New residential areas are more commonly adopting water-sensitive features, says Simon.
"There's not much data about how those perform over the long term but certainly it's a better approach than what we've been doing in the past."
A 2017 Ministry for the Environment and Statistics New Zealand report, looking at water quality, quantity, biodiversity and cultural health, found urban waterways had the worst overall water quality, including nitrogen.
Auckland Council's Healthy Waters general manager, Craig McIlroy, says the council and Watercare have implemented a Safer Networks programme to review the city's wastewater system.
"It may not require major infrastructure. It may be some houses have got their downpipes illegally hooked up to the wastewater system which is causing overloading. It requires a very detailed property-to-property assessment to track down the problems."
Community education, too: "This is not just a council issue, this is a societal issue that we're dealing with. The amount of litter that ends up in our waterways ends up in our harbours – that's all put there by humans."
The chair of the council's planning committee, Cr Chris Darby, says a quarter of the region's impervious surfaces are roads; run-off is a significant contributor to Auckland's water quality problems: "That has significant environmental impacts so we're asking AT [council-controlled Auckland Transport] to take responsibility for the environmental impacts of transport in a much clearer way.
"We're asking them to address how they design in the future, so that we can become more of a 'sponge city' and retain much of the stormwater generation on site, or within the vicinity."
Darby says some work has been done on a council design template that addresses many issues – "like streets that are fit for purpose for people, rather than just movement of vehicles... creating that 'sponge street' rather than a hard street that just sends everything to the curb, cesspit, stream, pipe, coastal marine area."