Abstract: Declining rate filtration systems using influent siphoning for influent flow to a bed of particulate filter media are improved by using at least two influent siphons with each filter bed. In use of such improved systems, influent is siphoned from a flume source or the like to the filter bed after backwashing of the filter media through a first siphon and, thereafter as headloss in the filter bed increases, further influent from the source is siphoned to the filter bed through a second siphon that has an effective minimum cross-sectional area substantially greater than that of the first siphon.