High volume flush vs. low-flush water closets and solid waste transport distance: a comparative study

Abstract

Upon the enactment by the United States Congress of the 1992 Energy Policy Act, it became mandatory that all water closets in residential and commercial settings reduce the volume of water that they consume per flush. In 1994, after installations began of the new low-flush or low-flow water closets that used less than half the water that their predecessors used, many owners of the new plumbing fixtures began to complain that their performance was sub par. Many complained about plumbing backups and of complete bowl clearance problems. There have been studies conducted to evaluate the new water closets’ bowl evacuation properties. This study focuses on what happens to the solid waste that is flushed through the water closet after leaving the bowl, namely how far the solid media is transported down waste piping. The main focus of this study is to compare the performance of the low-flush, 1.6 gallons (6 liters) per flush water closets with the performance of the formerly standard flush 3.5 gallons (13 liters) per flush in regards to how far they transport solid waste through waste lines. It was found that the media flushed through the high volume water closets traveled significantly farther that the media flushed through the low-flush water closets. It was often more than double the average distance. It was also found that media traveled farther down pipes composed of PVC than those composed of cast iron and also traveled farther down three inch pipes than four inch pipes.