Jason;
On the surface, we normally believe that our water usage is related to the pump PSI,; however, this is not always the case. For example, the more common, 100-135 psi pump does not produce alot of GPM in the first place. What may be happening is that it is taking more flushing action (causes greater water usage) for you to get a carpet clean because you may not have enough---or the right--kind of vacuum/extraction performance.
Yes, I have focused more on "vacuum extraction" in this case.
It may be true that the right kind of pump, using the proper GPM, with the right sized jets causing the proper and effective impact on the carpet is truly important, we tend to over-look the importance of the Extraction element. (And, this is why you had mentioned a TM)
Once you increase the air-flow in your extraction process, increase the impact (in a reasonable amount of PSI & GPM), you will actually clean faster; better results; and use alot less water! I know this from my own experience in the field, and when comparing smaller extractor with higher performing ones.
In conclusion, there are "High-performance machines"(Portables) out there that will help solve your problem. Keep researching!

Good Fortune to all;
Ed Valentine
cross-american corp.