What is deuterium-depleted water actually used for?
When you perform 1H-NMR spectroscopy in solution, there are many cases where you want to use deuterated solvent, so that signals coming from solvent hydrogen nuclei don’t interfere with the signal from your target molecule. Hence the frequent use of deuterated water, deuterated acetone, deuterated methanol, and deuterated chloroform. Aprotic solvents are also in common use, including carbon tetrachloride.

The situation is reversed when you want to perform 2D-NMR: you then need deuterium-free solvents, so their signal doesn’t mess with the molecule you're interested in. Hence, you will be interested in buying deuterium-depleted water.

(If you're wondering about real use cases for solution deuterium NMR, you can browse the literature for articles, there are plenty. One recent exemple is this one.)