The data provided that relates the various strengths of mortar to the amount of water that is used in the mix.
Here, the amount of water used is the independent variable and the strength of the mortar is the dependent variable. Generally, the independent variable is plotted on the x-axis and the dependent variable is taken as y = f(x) and plotted on the y-axis.
A suitable scale would have to be used to accommodate all the values on the axes. Also, the values on neither axes have to start from 0; you could start plotting the values on the axes from a point that lies at the lowest value you have or slightly below it. That would avoid wasting space and give a clear graph.