Much of this will depend on the mooring itself and the amenities provided by the mooring field. I Boot Key Harbor, Marathon Key, Florida, there are weekly pumpouts included with the mooring fee of 300. Extra pumpouts are an additonal $5.
Water at the city dock is .05 per gallon and metered. Also included in fee is free showers, free dinghy dock, free parking spot for their car and free WI-FI.
I knew about a dozen folks that lived aboard down there who worked full time jobs in town. Some had children living aboard with them, some had dogs and cats, and all showered daily.
Now, these folks worked at West Marine, some worked in restaurtants, one was a trash truck driver for the city. In my case, as a musician/singer/entertainer, I only stayed on a mooring ball for about a month, then tied up to the marina bulkhead so I could run my AC and keep the moisture off my delicate electronic gear, keyboard, amp, etc..., all of which I was transporting by dinghy for that first month. I only had one time where water splashed over the side of the inflatable, but it was scary - could have cost me thousands in damages had it been worse.
I have a 75-gallon freshwater tank, which lasted me about 2 weeks while on the mooring. I showered every day, and I had a shower head that conserved water while still providing a nice, hot shower. I also had a 5 gallon solar shower, which I filled from the freshwater tank so I didn't have to run the engine to heat the shower water.
Hope this helps,