Thus, one could couch a quality criterion that as little area of the garden as possible stays unwatered or that as little area as possible outside the garden gets watered.
Alongside a solution could be regarded as being ideal when as few as possible TVR are used to water the garden in an acceptable way.
In this case, the term acceptable would have to be defined as well.
In all cases, it is difficult proving that a solution is ideal and within the students’ solutions this can surely not be expected in a general form.
In fact, the students’ approaches are affected by a mixture of geometrical calculations as well as plausibility assumptions.