Do Cruise Ships Dump Sewage? Yes. To get into a few more specifics than above, the U.S. allows cruise ships to dump treated waste into the ocean if they are within three and a half miles from shore. Beyond that point, there are no restrictions for dumping untreated, raw sewage in U.S. ocean waters.

On a modern cruise ship, sewage (known as "black water") undergoes an incredibly sophisticated treatment process that often results in water cleaner than what comes out of many municipal tap systems. When you flush a toilet, the waste is vacuum-piped to an Advanced Wastewater Purification System (AWPS). First, the sewage is filtered to remove large solids. Then, it enters a bioreactor where aerobic bacteria break down organic matter. Following this, the water goes through a "membrane filtration" process to remove microscopic impurities and finally is treated with ultraviolet (UV) light to kill any remaining pathogens. The resulting "effluent" is so pure that it can be safely discharged into the ocean while the ship is moving, provided it meets strict international and local environmental regulations. The remaining solid waste (sludge) is either dried and incinerated at extremely high temperatures onboard or offloaded at specialized port facilities to be used as fertilizer or fuel. Modern cruise lines are prohibited by international law (MARPOL) from dumping raw sewage into the ocean, and most high-end ships today far exceed these legal requirements, using technology that minimizes their environmental footprint significantly.