A historical and critical review of latrine-siting guidelines

Latrines are an effective way for people in low- and middle-income countries to move away from open defecation. Guidelines are used to provide a recommended horizontal setback distance from a latrine to a downgradient well to ensure the safety of the well from subsurface contaminants. We collected 107 journal papers, books, and reports to critically review the recommended setback distances and how these recommendations are derived. It was discovered that the four most common guidelines/reviews are all based principally on just four field studies, all of which were conducted over 40 years ago, which casts doubt on a frequently used one-size-fits-all approach. More recent methods for latrine siting use both field data and some sort of modeling component to account for the different site conditions, but these models have not been verified for use outside their respective studies. They are also limited in how they consider the hydraulic connection between the latrine and the well. We recommend that future siting guidelines should focus more on vertical separation, include chemical contamination, and be based on models describing how latrines and wells are hydraulically connected, along with the fate and transport of potentially harmful contaminants. HIGHLIGHTS Most common guidelines are based on four field studies, conducted over 40 years ago.; Latrine-siting guidelines must account for the vertical transport of pollutants.; Siting guidelines should account for the distinct features of loadings and transport of bacteria and viruses.; In situ treatment technologies and resource recovery strategies may influence pollutant loadings.; Models can assist with site-specific siting.;