I've recently developed a system that only uses about 15 litres of water per day, costs a minimal amount to run, and doesn't require expensive filtering equipment.
Step forward and take a bow - the t-bar applicator and bucket.
Available in a variety of colours it is durable, doesn't require a van with a high payload, and is readily available in most janitorial supply shops. No taps or hoses needed. Simply take your 3.5m double section ladder, extend it upwards, and start climbing.
I have many satisfied customers, such as Fred here:
TESTIMONIAL
Fred: "Until I bought Walter's ladder and bucket system I was lacking fitness, overweight, and shelling out loads of money on new tools and consumables. Now, for under £200 per year and using less than 15 litres of water a day, I can climb, keep fit, and get paid for it too. I would recommend Walter's system to anyone. It really has changed my life. I even receive NHS cover for broken legs when I fall off."