Sizing by household
Rule of thumb: 1 gallon per person per day for drinking and cooking. Two-person household needs 2 gallons/day -- the Travel Berkey or Big Berkey handles this easily. Four-person household needs 4 gallons/day -- the Big Berkey at 3.5 GPH (2 elements) produces 84 gallons/day at its capacity to filter; the 2.25-gallon upper chamber is the real throughput limit. For households that refill the upper chamber frequently and have time, the Big Berkey is adequate to 6 people. For households that prefer fill-once-per-day operation, size up to the Royal Berkey at 3.25-gallon upper chamber.
Fluoride removal add-on
Black Berkey elements do not remove fluoride in the standard configuration. If fluoride reduction is needed, add Berkey's PF-2 fluoride filter elements, which attach to the bottom of the Black Berkey elements and specifically reduce fluoride (and arsenic). The PF-2 elements have a shorter life (1,000 gallons each vs 6,000 for Black Berkey) and add $50-$80 per pair to the system cost.
Berkey vs Waterdrop RO
Berkey: no electricity, no waste water, removes bacteria and viruses, retains beneficial minerals, slower throughput (gravity-fed). Waterdrop G3P800 RO: requires electricity, produces waste water (1.5:1 ratio), removes fluoride and nitrates (which Berkey cannot), faster dispensing (pressurized), requires installation. For off-grid or emergency use, Berkey is the correct choice. For primary kitchen filtration in an owner-occupied home with access to electricity and plumbing, Waterdrop G3P800 provides more comprehensive TDS and fluoride removal.