Just hooking the hose up to the pressure washer. Yes, it adds water, but not all that much. Its mostly air/pressure. works great. I got rid of some water through "waste" on my filter, but it wasnt that much. I had a terrible problem with CYA two yrs ago when I had the pool put in(thanks to the pool store) but after converting to the BBB method last summer, finally got it into a more manageable 60 range and adding and removing water still helps it. My IG pool does not have "eyeballs" to turn up to help with aeration. I read somewhere on this forum where they used a pressure washer to raise their PH and I put it to use today. I dont take my PH any lower than 7.2 due to my vinyl liner. I dont like to take chances. The BBB method has helped me maintain a beautifully crystal clear pool. I am so glad I found this web site. I missesd my PS annual spring sale of chemicals - darn, tee hee.