The majority of properties in England and Wales are connected to the public sewerage system but an estimated 4% of properties depend on independent privately owned and operated systems.
Mae’r rhan fwyaf o eiddo yng Nghymru a Lloegr wedi’u cysylltu â’r system carthffosydd cyhoeddus ond mae rhyw 4% o eiddo yn dibynnu ar systemau annibynnol sy’n eiddo ac o dan weithrediad preifat.