The Grove water sensor fits perfect in the hole of the boat.
The boat prevents the drowning of the elektronics what could have happened if the sensor was fixed at a wall.
The boat has a arc on each side so the water can flow to the sensor
This is made to left just a bit of water in the tank, the sensor tough the bottom almost when the legs are on the bottom. If you remake this with higher legs then you decide how many water there may be in the recipient before its detected.
Movies about the working : https://www.youtube.com/watch?v=T8rrHqp7u80