Sewage is one of the top pollutants of Barton Springs. Raw and treated sewage contaminates the aquifer through leaky lines, spills, leaky septic tanks, and "wastewater irrigation." There are over 25 sewage treatment plants permitting or proposed in the Barton Springs watershed, disposing of over 3.6 million gallons per day of treated sewage. This figure is not including City of Austin sewage lines that transfer million of gallons of sewage per day to treatment stations.

Many subdivisions, old and new, build their own small sewage treatment plants to treat the "waste" water that flows from homes. Then where does the wastewater go? Frequently it is sprayed onto or under undeveloped parts of the subdivision in the open spaces and greenbelts, a process known as "effluent irrigation" or "land application" of sewage effluent. This wastewater contains pollutants that can harm the creeks, aquifers, springs and wildlife if not completely absorbed by the soil. When soils are saturated from our hard hill country rains, wastewater is at risk of reaching the groundwater and creeks, polluting the aquifer.

The Belterra subdivision has recently proposed an even more damaging wastewater disposal system, known as "direct discharge." This system would put Belterra's sewage directly into pristine Bear Creek, one of the major creeks that recharges the Edwards Aquifer and Barton Springs.