Water is retained by the high soil organic matter content [Ed: and additions of biochar] and evaporation is limited by mulching and dense planting. Watering requirements are thus significantly reduced compared to a conventional approach.
To supply a permaculture with water, priority will be given to soft solutions like pond creation and rainwater harvesting (roofs of greenhouses and buildings), rather than a borehole and a pump. Each garden should ideally have one or more pools. On sloping ground, it is desirable to dig ponds as high as possible so that water can then flow by gravity.
[Ed: Bec Hellouin microfarm has a stream running through it, so it may have missed out on the full range of watering problems. In drier situations, there would be more to say about efficient water provision. The works of David A Bainbridge on “super-efficient irrigation” are a good place to start: https://works.bepress.com/david_a_bainbridge/. He covers various ways to apply three basic principles individually or, better, together: Bypass the Soil Surface; Deliver Only to the Root Zone, Deliver Only the Amount Needed. Notice that these also limit competition from weeds.]