Miami sits upon the huge Biscayne Aquifer formed from porous limestone that both stores and purifies the cities drinking water. But it is incredibly fragile from both human made contamination by industrial or mining activities, and from climate change that raises sea-levels and inundates the aquifer with runoff from the city.

This most complex of water systems is in a fragile balance and a recent Bloomberg article states that "Climate change is slowly pulling that machine apart. Barring a stupendous reversal in greenhouse gas emissions, the rising Atlantic will cover much of Miami by the end of this century."

More immediately though - "In 2014 an EPA report warned that 'flooding from more intense and frequent storms' could push toxins from Superfund sites into underground water sources like the Biscayne Aquifer."

So the cities water supply is threatened from two directions - sea water intrusion from sea level rise, and from run-off of toxins into the aquifer. But there is another problem - Septic Tanks. "As developers built out Southeast Florida, they found that instead of connecting each new home to the local sewer system, it was often easier to install septic tanks. Miami-Dade has about 90,000."

Where development occurs too far from main utility connections developers provided on-site storage with Septic Tanks. Properly serviced and maintained a septic tank can last up to 50 years with minimal environment impact assuming that the accumulated sludge is removed and disposed of properly. However the liquid produced that filters out of the septic tank into the ground where bacteria are normally filtered out naturally is a problem in Florida due to the very high, and rising, water table. Another symptom of the modern age is that our faeces are not as natural as they once were and contain high levels of pharmaceuticals. Ironically these are used to track the spread of septic tank overflow within the aquifer.

"Homes with septic tanks could be connected to the sewer infrastructure, a process ... [estimated to] cost from $2 billion to $3 billion." But is there a better way?

Small water up-cycling plants within neighborhoods could take the effluent from homes that would otherwise discharge into septic tanks, and re-use the water as flushing water. This would reduce the demand for water and remove the risk of liquid contamination of the aquifer - and at a much lower cost than connecting all of the areas to central sewage treatment. The failure mode would also be a lot lower as no single point of failure could cause a problem to the treatment of waste.

The money saved could then be used to address the other sources of contamination - superfund sites, sea water ingress and the need for desalination plants. More urgency should also be given to the Everglades Restoration Plan that will push more clean fresh water into the aquifer from the west and so push back against salt water infiltration from the Atlantic on the east.

And money is the problem. There are huge demands upon the budget to deal with these and related water quality issues. We believe that small initiatives spread widely with local accountability and funding can do much to reduce the drivers of cost caused by large centrally planned and funded projects. These will still be needed, but local problems should be managed locally first.

Update: 21 Feb

The Biscayne Aquifer is threatened by a recent ruling by the Florida First District Court of Appeal that appears to allow drilling in the Everglades through the limestone structure of the aquifer. Any contamination may have widespread effect as detailed in the article on City Lab. Although water upcycling is a different subject this article covers in detail how vulnerable the aquifer is to contamination. Oil drilling is a clear and active threat but failing septic tanks remains an ongoing problem that no court order to stay their operation will resolve. Strong action to replace the tanks with waste water treatment will solve the problem.