Even with a 200 gallon tank you will need to use the home's water source.
The only thing that matters is what is the gallons per minute flow at your customers? If the worst 20% of your clients can still provide 6 gpm in your market, then you can get by with really small float tank. About 90% of our customers have 6 to 8 gpm, most of the rest are right about 4 to 6 gpm, and then a small percentage (mostly windsor heights) has about 2 to 3 gpm. One of our vehicles has a 15 gallon float tank and the other has a 100 gallon float tank. I don't schedule jobs in windsor heights for the first vehicle. And even the 100 gallon tank would run out on bigger jobs in Windsor heights.