Low pressure but passive, resilient to pump/power failure.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
Elevated storage above the shower for adequate gravity pressure
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.