Why can we not use water instead of blank control solution in enzyme catalysis with Peroxidase experiment?

I have to do a lab about enzyme catalysis with peroxidase in my chemistry class. We are to use the blank control solution in the experiment. My question is, why can we not use water instead? I did some research about this and someone says something like "It is because the water blank absorbs so much light that the usable scale is compressed, thus, causing a poor accuracy." Is this the exact reason why we do not use water in this experiment?

1 Answer

It is because the water blank absorbs so much light that the usable scale is compressed, thus, causing a poor accuracy.

For water, the absorption coefficients $\alpha\ [\mathrm{m^{-1}}]$ at $\lambda$ = 680, 580, 535, 480 and 380 nm are 0.47, 0.09, 0.045, 0.013 and 0.011.

(Source: R. M. Pope, E. S. Fry, Applied Optics, 1997, 36, 8710-8723)

That is not a lot.

On the other hand, you never know about impurities in your buffers or other components (apart from your probe).

Therefore, you usually do not measure against "just the solvent", but against the solution of "everything except the probe" to record the complete background.