The public washrooms (service pavilion) at the very busy Vincent Massey Park in Ottawa, Canada, harvest rain water for over 90% of their needs. That's the water used for the low-flow toilets. The urinals in the men's washroom require no water and the taps at the sinks use regular treated potable water supplied by the local muncipality.
All the rain water that falls on the large roof pours down the sides to gratings that lead to an underground cistern (storage tank.) When water is needed for a flush, it's sent up to the toilet.
Other features - lighting and electrical power
Much of the lighting is sunlight. As the photo below shows, the day I was there taking pictures the electric lights weren't even on. All lighting was coming from a skylight and from sunlight coming through the walls.
27 photovoltaic panels (solar electric panels) supply power to the local electrical grid/power utility. Meanwhile, electricity for lighting, the hand drier and pumps for pumping water from the underground cistern comes from that same electrical grid. More power is generated than is used so the pavilion is a net-zero electricity user.