Confirmed (permit record)
Likely (inferred)
Faint = low % septic · bold = high % septic
Circle size = raw count (secondary)
17M+ septic systems nationwide, from
PermitLookup.
Florida comes directly from the state DOH source (confirmed permit records);
other states are inferred from property and permit signals. Confidence varies
sharply by state — some are 95%+ real permit records, others (e.g. Wisconsin)
are mostly statistical inference. The legend distinguishes the two. Zoom in
for individual systems.