For many two-bathroom homes, a 10-inch iron/sulfur filter around 12 GPM service flow is a practical starting point. SpringWell WS1 and RKIN WF10 both sit in this class, but the well pump must also support the filter’s backwash requirement.
Size from household demand
Two bathrooms often fit comfortably in the 10–12 GPM service-flow range, but high-flow showers or simultaneous fixtures can push demand higher.
Backwash flow is the hidden requirement
Regenerating iron/sulfur media must periodically backwash at a substantial flow rate. A filter can look correct for household service flow and still be a poor fit if the well pump cannot support cleaning flow.
Manufacturer reference point
SpringWell WS1 is currently rated 12 GPM service for 1–4 bathrooms. RKIN WF10 is also rated 12 GPM for 1–3 bathrooms.
Test water before sizing
Iron, manganese, sulfur, pH and hardness affect treatment choice. Bathroom count alone cannot determine whether an air-injection filter is the right technology.