This problem involves the knowledge of mathematical modeling. If it's a perfect model, it's very complicated, and you probably can't work it out. There are basically three coefficient relationships when writing a paper or writing it yourself.

First, water consumption V (L).

Second, the clothing weight m (this model does not consider the degree of stains)

Third, laundry time t (minutes)

Suppose the mass of washing powder is m(g)

The relationship is as follows

m=v+m^2-βh/3； (Tap water in general cities is hard water (β = 1.87) and soft water (β = 3). This is what I saw in modeling before. Please check it.