DELAND — As the population continues to grow and sea levels continue to rise, Volusia County residents over the next few decades can expect their relationship with water to change. Not necessarily for the better — unless changes occur.

Last week, at the annual State of Our Water conference sponsored by the Volusia Water Alliance, scientists, educators and other local experts addressed challenges to the county's waterways.

Among the biggest challenges is nutrient pollution, which occurs when nutrients, primarily nitrogen and phosphorus, end up in water, causing algal growth.

"Not only is it an environmental disaster, but it's an economic disaster," said Lisa Rinaman, chief at the St. Johns Riverkeeper, a nonprofit that works to protect the river and educate people about why the health of the river matters.

Locally, fishermen and environmental advocates have expressed concern about the proposed Mosquito Lagoon Reasonable Assurance Plan — a joint effort by the county, Edgewater, New Smyrna Beach and Oak Hill — lowering water quality standards and not doing what's necessary to protect the lagoon and restore the water's quality.

[READ MORE: County may seek compromise with opponents of Mosquito Lagoon plan]

Septic tanks, one of the main causes of nutrient pollution, account for another matter that cities are trying to sort out as the population and pollutants grow.

The unsustainable practice of permitting the dumping of biosolids, a byproduct of wastewater treatment facilities, near the headwaters of the St. Johns is undermining any investments that have been made in protecting the river, Rinaman said.

Utility companies often contract with third-party haulers to get rid of the waste on the cheap by having it taken to and spread on agricultural lands where the state has sanctioned it can go, according to Jimmy Orth, executive director at the St. Johns Riverkeeper.

"Unfortunately that sewage sludge has to go somewhere," Rinaman said. "You can't just relocate the pollution from one watershed to another and expect for there to be a different outcome."

The solution is simple, Rinaman said.

"Permit applicants must affirmatively demonstrate that the phosphorus in the biosolids will not add to phosphorus loading in the St. Johns River or its tributaries," Rinaman said. "Stopping pollution at its source is cheaper and has better long-range benefits and it makes sure that we're living within our means."

As nearly 12,000 people move to Volusia County each year, cities are reckoning with the number of septic tanks they have.

"Septic tanks have a function, but we never really expected to build out at this level and this concentration of septic tanks, and for the record we're now at 107,000 septic tanks in Volusia County," said Clay Henderson, executive director of Stetson University's Institute for Water and Environmental Resilience.

That's a large number of septic tanks for a county the size of Volusia, said Michael Ulrich, director of Volusia County Water Resources and Utilities.

Scientists have found that septic systems are a major contributor of nutrient pollution. Systems that haven't been properly maintained can lead to contaminants getting into surface and groundwater.

The state is working to combat this with grants for septic system upgrades for eligible homeowners in multiple counties, including Volusia County.

Henderson said advanced wastewater treatment should be required for septic tanks if communities don't want to switch to sewer, which tends to cost residents more. 

Advanced wastewater treatment plants are pricier, but they remove nutrients such as nitrogen and phosphorus as well as a high amount of suspended solids, per the Institute for Sustainability, based in New York.

Not forcing residents to switch from septic to sewer has been one of the main talking points for City Commission candidates in Deltona.

The city passed an ordinance earlier this year stating that it wouldn't force residents onto sewer. But some candidates said they would rather change the charter and put the concern to bed, once and for all.

Reducing usage of septic tanks isn't the end-all solution, though, Rinaman said.

"Once we take septic tanks offline, if they're going to a wastewater treatment facility and then the byproduct, the sewage sludge is going on our land adjacent to our wetlands and waterways, we're shooting ourselves in the foot," Rinaman said.

[OUR VIEW: Deal with reality of changing planet]