A waterjet system in accordance with a particular embodiment includes a pressurizing device configured to pressurize a fluid, a cutting head downstream from the pressurizing device, and a catcher positioned to collect a jet from the cutting head. The system can further include a treatment assembly configured to treat a feed fluid to the pressurizing device and/or a byproduct fluid from the catcher, such as by removing submicron colloidal particles from the feed fluid and/or from the byproduct fluid. For example, the treatment assembly can include a coagulation unit, such as a chemical coagulation unit or an electrocoagulation unit, configured to coagulate the submicron colloidal particles. The pressurizing device, the cutting head, and the treatment assembly can be at different respective portions of a fluid-recycling loop.