Ian,
I know your a web designer and in Theory it sounds a very good idea, but this will only be of service to the minority of your customers and to those who really give a dam on how you clean there windows.
My advice that worked very well for me, with NO loss of customers, is to talk to each and every one of your customers, take the time out to explan the EU issues regading the use of ladders, and what you plan to use in the future, ie poles and explan about the pure water.
Do it months before you change over, dont just turn up on there doorstep and expect them to except your new method, or you will loose customers, also take this time to clean all the frames of your customers windows while your up your ladder.
When your ready for the change over, issue each and every customer with the explanation letter, it serves to back-up what you have already explaned.
Doing all the above is called customer relations and winning your customers trust, you as an x salesman should already know about winning there trust, once you win there trust, your foot is in the door.