> Also was wondering if anyone had suggestions for setting up a recycled tub, that is to say the water can be set to run back after running out, so that it does

> Also was wondering if anyone had suggestions for setting up a recycled tub, that is to say the water can be set to run back after running out, so that it does not cost excessive amounts. Unless you actually have a cost issue (do the math on that) there already exist a really good water recycling system in many developed countries https://en.wikipedia.org/wiki/Reclaimed_water https://en.wikipedia.org/wiki/Reclaimed_water even if it doesn't exist where you are, water is not lost due to the water cycle. In many places domestic water use is a negligible part of the water supply issue, don't be guilted into messing with your childs development for that. I would generally teach the children to turn off water after it is done, to not leave the room if water is running and how to prevent flooding and how deal with flooding. If cost is actually an issue a simple variant to reduce that cost without reducing agency is to have a simple mechanic constraint how far the tab can be opened that is tamper obvious. If those mechanisms are damaged address that issue . Reinforcing is possible but also increases the risk of damage to faucet which is going to be a lot more expensive. Water toys which use less water but also have an acceptable spilling risk could reduce water use. This could be anything from a digital circuit using water logic that just stops doing something interesting or an analog computer with a limited capacity before it fills up whose drain rate is small or requires adult supervision (lock) to drain. Closed containers with fluids might also be interesting. Such as non mixing differently colored fluids which in a drop proof container. If you want change the amount of water allowed in a way depending on good behaviour a 3d printing pen would allow to construct tamper obvious mechanical constraints with different amounts of reinforcement which are unable to be removed without breaking in most tabs.