Is there a rule of thumb to determine buffer tank size when using an 8 or more GPM pressure washer?

The question is in regard to residential and possibly light commercial. I’m new to the game, and just trying to figure out some of the things I’m unsure of. If you have an 8 GPM machine and your supply is providing 7 GPM, you’re only working at a 1 GPM deficit, so it would seem pointless to have a 200 gal buffer tank since that would allow over 3 hours of trigger time before you ran out of water. If your supply was only providing 4 GPM that same 200 gal tank would allow 50 min of trigger time.

I’m guessing you have to know what your typical supply GPM is, and how much consecutive trigger time you need? Or is there more to it than that?

Three hours isn’t that long, especially when surface cleaning. I use a 225 gal leg tank. I usually have 100 gallons or so at all the beginning of the day and I’m still waiting on water sometimes.

Water is one of the things that it’s always better to have an excess than not enough. You can always shut off the supply hose.


Agreed. I have a 225 leg tank as well. If I’m surface cleaning, I start when the tank is half full and it basically stays there the whole time. Get the largest tank you can safely haul full, unless you’re feeding off of hydrants and can fill the tank in seconds

Sure, always better to have more water than less, but 3 hours isn’t that long? I didn’t mean over the course of the day, I meant being able to have the trigger pulled for 3 consecutive hours.

It was probably a bad example, as (at least where I live) I don’t see 7 GPM supply, ever. I just used 7 so I could show that a small 1 GPM deficit meant a lot of available trigger time without waiting for water.

I suppose you guys who have been at this for a while want to show up at a job have the trigger pulled within 2-3 minutes of arriving? I was more imagining showing up, connecting to the supply, and then getting set up and possibly going over a few things with the customer while filling the buffer.

I think that about sums it up. Figure out those two variables, and you should be good to make an informed decision.


I try not to ever haul water to sites. I’ve done it on a couple of houses that are on wells because I don’t want to stress their pump out too bad. But I have a tandem trailer with brakes and a leg tank that is secured like Ft Knox.
I pull up empty, say hi, start filling the tank. By the time the outlets, doorknobs, and Ring cameras are bagged, and my hoses are laid out properly, I’m ready to get to it.
The higher the water level in your tank, the happier your pump will be.

It largely depends on what your city environment looks like, I don’t think I’ve ever spent 3 hours doing a residential driveway with an 8 gpm machine, plenty out in the country suburbs with long driveways into a property but in the city it’s pretty rare. 80% of my driveways I’m in and out in 1.5 hours tops. For commercial it’s a little different and I charge by the hour, and wouldn’t hesitate to charge an extra hour for waiting on water. And to be completely honest I don’t think I’ve ever been on the trigger for 3 hours straight inbetween joking around with the boys and answering phone calls, moving hoses etc. (and neither have my guys, that I can assure you! :joy:)


Just because a spigot is giving you 7 gpm doesn’t mean it will the whole time you’re there washing. The second the homeowner throws in a load of laundry or runs the dish washer you might go down to 4 gpm or even less. Plus, flow rate can change from one house to the next. I might get 10 gpm at one house and the next one at the end of the dead end street is still on a well and only gets 3-4 gpm. I almost always travel with my buffer 1/4-1/2 full unless I know I’ll be working somewhere I won’t have to worry about flow rate.


Depends too on how much fill hose you’re running. On a 7gpm spigot if you’re running 200’ of 5/8" you’re going to get 3.5gpm of flow.

1 Like

Is there a way/ formula/ any literature that kind of explains this further? I’d love to read into that

Search “friction loss” on google or this forum here. Racers written plenty on it.

1 Like

I guess we have a difference in houses and driveways here. There are tons of 5-6k sq ft residential driveways in my town.

I guess I don’t understand what you’re trying to get at. Are you just trying to find a way to get away with a smaller buffer tank? If I could fit a 550 gallon tank on my trailer I would do it in a heartbeat.

Waiting for water sucks, period.

1 Like

One more bit of advice. Never plan on wasting time. You never know how you’re business is going to look in the future. I wash a lot for people who are at work or rentals. So on most of my houses there is no need to stand around a chat with anyone.

From pull up to actually washing should absolutely take no longer than 10 mins.

But you can put whatever size buffer tank on your rig as you want.

1 Like

I just measured mine. Ranch style house w/2 car attached garage. 56x16, so just under 900 sq ft. There aren’t any driveways 5-6x bigger than that in my neighborhood, but yeah, I’ve seen them, especially if the house is set way off the road, and bigger homes on golf courses with semi-circular drives

I have no doubt. I’ve never used a high flow commercial unit, just your typical homeowner low flow electric model hooked directly to the spigot, so I’ve never waited for water. I imagine it’s like being in your car and waiting for a long train or for a traffic jam to clear. Those are the kinds of thing that are at the top of the list of things that aggravate me, so I definitely don’t want to wait on water.

And hooking up a 100’ hose to the homeowner’s supply, in 10 minutes you’re not going to have filled your buffer tank much, so have some water with you. I get it. Thanks.

1 Like

Do you think 3/4" hose would increase the flow much? We sometimes have trouble with 8 GPM and 100 gal buffer keeping up with about 150-ft 5/8" supply hose.

This was calculated at 30 psi supply. I think the average for most houses is 40 psi but can very.

Cool, that is a pretty big increase in flow. Might as well give some 3/4" a try. Thanks!

Are you pulling your supply hose off the reel as well?

Here you go, play with it some

1 Like

A lot of us run 3/4” garden hose for supply to maximize flow. If you’re not already doing these things then change your setup to get the best possible flow rate:

  1. Use the shortest length of hose you can when connecting to water supply. I have 100’ of 3/4” hose coming off the reel first, then (2) 50’ hoses in case I need them. Everything has camlocks for efficiency. 100’ for me normally does the job.

  2. Don’t run the supply water through the reel as it reduces flow. Even if it was a 1” manifold you still run through the swivel at a 90 and at least a couple more sharp turns. Install a short 3/4” hose to the buffer with a camlock on receiving end and hook supply hose to that when stripped off the reel.

  3. If you’re not worried about overflowing the buffer tank then do away with the float valve if you have one installed.

  4. Hook up to 2 spigots (spickets) simultaneously for supply if you need more flow.

  5. If you have a water filter plumbed into your supply line then get rid of it. One quality filter between buffer and pump is all that’s needed for residential. I have one installed but I don’t usually have to wait for water.