One of the most important needs for a fully functioning permaculture design system is the use and availability of water. I have found articles in "A Designers Manual" by Bill Mollison, on water supply a really useful tool. Since the publication of "A Designesr Manual" some other important literature became available, among them, Brad Landcaster's 'Rainwater Harvesting for Drylands and Beyond". The previous mentioned books explain practical processess while videos from website "What If We Change" (http://www.whatifwechange.org) document practical applications of the process of how water infiltration and acquifer re-charging works. I'm using these ideas from these sources that I adopt to my needs as a designer. Example, using rainwater capture, infiltration and storage of water in the soil. The reason we store water in the soil is to alleviate using town water or piped in water.
I have experimented with recycling of grey water, composting toilets and acquaponics.