Most residential/commercial pressure washing companies will tap into the homeowners/businesses water supply. Getting companies to bring their own water is a possibility however getting trailers of water is more expensive than hooking up to your source of water. Most companies have their own water tank on their truck but only bring somewhere between 200 to 400 gallons with them to start the job. If you are on a well this can be more taxing on your system and you might need to buy a bulk tanker of water. Always make sure you talk to your pressure washing company before they come out and hook up to your water. Ask them how long they will need to run your water and how much water they will be bringing out with them.