 When the soil is permeated by sewage from leaking sewers or from other sources, then leaky pipelines will be infiltrated with contaminated water when pressure is low.According to the Federal District's water quality laboratory, neighborhoods that experience more frequent interruptions in service have poorer quality water compared to neighborhoods with a constant supply.The percent of household tap samples in compliance with the residual chlorine standard (0.2 milligrams/liter) ranged from 87 to 100 percent in tests undertaken in 1993 and was notably low among southeastern counties (Iztapalapa, Tláhuac, and Xochimilco).