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I hope you're using a surface cleaner, that's a long drive at 2600ft. What kind of power washer do you run? 200 gallons might clean a couple thousand square feet depending on your setup.  If you run 400 feet of garden hose from the house to the tank, and 400 feet of supply hose from the tank to the power washer and 400 feet of high pressure hose, your only half way there and suffering major supply issues and pressure loss. With my set up (trailer mounted) I would fill up my tanks (650 gallons), drive within 400 feet of the end of the driveway and run 400 feet of high pressure hose. Working my way toward the water supply, I might have to refill my tanks several times (a huge time killer) before I got the truck supply hose within range of the water supply.  You might look into a nearby fire hydrant to supply water.  I've done a bridge smaller than this but we had unlimited water from the river below.