That's not bad. We did an 18 day ocean crossing from the Galapagos to the Marquesas on one 150 gallon tank after the watermaker got polluted with fish oil the night before we left.

We used the tanks just for showering and washing dishes, water for drinking and tea came from bottles of watermaker water stored before we left.

We could have used less if really required but that would have meant cutting out showers.