A study in Portugal looked at why drip irrigation systems get clogged when using waste water from treatment ponds. They tested five different designs and found that ones with long, winding paths worked best. Sand particles were the main cause of clogging, with algae playing a smaller role. The design of the emitter, not the water quality, was the most important factor in preventing clogs. It was concluded that algae from the ponds isn't a big problem for drip irrigation systems, as long as steps are taken to keep sand and soil out of the pipes. Recommendations were made to prevent clogging in future projects.