What about making a 10 or 15 gallon buffer tank with a float set up. Hook it up to your machine and put the hose right to the tank. Wire the float to kill the engine when the float drops too low. At the end of the job you shut off the water and purge your hose out and maybe the hoses if needed. You don’t have to empty it all. Just enough to be easy enough to carry it.
It’s a bit much to make but it’s better than a $700 CAT pump.
I encountered low flow recently, and even though I’m new to power equipment, I could tell instantly my pump wasn’t getting enough water. It made this ‘errr’ sound and I released the trigger right there.
I haven’t been on my first job yet still reading and reading some more when I don’t want to, but the general consensus I’ve seen is to be over prepared for the job. get a proper water buffer(125 or 275 tote) and just be ready for the customer to do whatever they want. You’re providing a service to them and it’d behoove you to be professional enough to account for someone deciding they want to wash dishes or shower.