A bucket of water can be kept clean until it runs out.
If you quickly dip your applicator into the water and then wring it out on the floor the water will stay clean.
If a cloth gets to dirty to use then get a fresh one rather than put a dirty cloth in your bucket.
My water was getting filthy all the time until I was given thse tips. Of course these tips wont work for everybody, it depends on what methods you use to clean the windows.