At Portland we've had the orange desert sand all over the boats and this coupled with the exhaust soot from the Helicopters using the training base makes for a messy mix. Cleaning the screens before and after trips, paying attention to the wipers is essential - that sand is very abrasive. If you leave this mix in the non slip areas it can be a nightmare to remove. So it will be the buckets, sponge and stiff broom.
You will probably find that a hosepipe ban will not apply to the marina facilities / services and they will be more than willing to charge a lot of money to clean the boat for you - using the same or more water than you would!