Water mains access cover from the time Amsterdam had two water sources: dune water and water from the River Vecht. The water supply from the Vecht was established in 1888.
Links (left) and Rechts (right) refers to the turning direction of the water valve.

See here for more info (in Dutch):
www.geheugenvanplanzuid.nl/index.php/architectuur/401-trottoirs-qduin-rechtsq