I started out like that 15 years ago and didn't have a tank for first 5 years and 7 years before a generator

I never had a problem and did 95% of my business at residences. Once I got tank and generator though it was 95% at businesses. One thing you'll notice is you have to turn away business when they don't have access that you can use or reach. An economical alternative assuming you have a car is
A small tank or carry 6gallon water containers (similar to gas), anything you can hold water in that is cheap. At first I had a 30gallon plastic drum that I got from a Army surplus store ($5 or $10). You'll need a 12volt pump or electric pump. These will run you $30-80.
Instead of a generator you can use a 750watt invertor (Walmart around $60-70) and a 1 gallon shop vac. Friend of mine uses that set up. If you have the invertor you can get small electric water pumps a little cheaper than the 12volt ones.
You don't need a large vehicle, just need to be creative with your space. I started in a 1990 plymouth laser and then a 1992 plymouth colt hatchback. I like the 6 gallon water containers as you can fill those inside anywhere and they are easy to put in and take out. I think they are $6 at walmart.
So for about $150 you can have power and water with you. You could still use customers stuff when it was available.
Some use QEW and love it. I've never used it but that would elliminate needing the pump. A cheap alternative to the vac and invertor is a 12volt vaccum. They take a while to do but when you are starting out you'll have more time than money usually.