Silver-impregnated ceramic candle or pot filter (e.g. the Filtron design developed with Potters for Peace) removing particulates and the large majority of bacteria by gravity flow alone, no power or pump needed. Slow, roughly 1-2 L/hour per candle, and doesn't address dissolved chemical contaminants, but keeps working during a power or pump outage and can be produced/repaired locally.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
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.