Drainage, Waste & VentQuestion 139 of 360

Under the CPC, rainwater (storm) drainage and sanitary sewage generally must…

a.share the same building drain
b.combine at the building trap
c.be kept in separate piping systems and not combined unless a combined public sewer is approved
d.combine only if the pipe is upsized

Explanation

Storm and sanitary drainage must be kept separate; rainwater must not discharge into a sanitary sewer, and sanitary waste must not enter a storm drain, unless the jurisdiction has an approved combined sewer. Combining the systems can overload the sanitary sewer during storms and cause backups. Where a combined public sewer exists, connection rules are set by the local authority.

Law Reference: 2022 California Plumbing Code (CPC) §1101.0

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