Other ingenious waste collection methods such as the Liernur system presaged vacuum toilets that are now seeing a renewed interest. Within this scheme, household toilets were installed with cast iron pipes that went underneath the street in a zigzag formation and poured into a reservoir. A vacuum pump powered by a steam engine created negative pressure in the pipe system to suck away human waste, so rinse water was unnecessary and even undesirable. As soon as the reservoir was full accumulated sludge was then sold directly to farmers and gardeners or brought to a pourette for drying(Mulder, 2016). Liernur systems saw widespread adoption in London and Amsterdam, (Halliday, 2013) which by 1900 had over 120,000 connections(Mulder, 2016). Nevertheless, with the introduction of chilisalpeter (nitrate) for fertilizer, human waste collection for agriculture became obsolete, and the Liernur system quickly fell out of use.