Whole House Flow Rate by Bathrooms and Occupants

The peak gallons per minute a house has to pass, which is what decides the filter housing size. Fixture flow rates are federal maximums; the bathroom count method is trade convention.

Every page below is computed rather than written, from the same formulas the matching calculator uses, so a figure on a chart page and the same figure in the calculator cannot disagree. Each one carries its working, the basis of every number it prints, and equipment chosen by those numbers rather than from a general list.

Researched, not professional advice. Every figure on these pages is labeled as a published standard, a trade rule of thumb, or something that can only come off your own water test. Where a published figure does not exist we say so rather than estimating one. Test your water before you buy equipment: on city water start with the Consumer Confidence Report your utility publishes each year, and on a private well only a certified laboratory test tells you what you have. Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics and need a laboratory and usually a licensed professional.