40 CFR 139.26: Pools and spas.

(a) The requirements in paragraphs (b) and (c) of this section apply to discharges from pools and spas.

(b) Except for unintentional or inadvertent releases from overflows across the decks and into overboard drains caused by, but not limited to, weather, vessel traffic, marine wildlife avoidance or navigational maneuvering, discharge of pool and spa water must:

(1) Occur only while the vessel is underway, unless determined to be infeasible; and

(2) Meet the following numeric discharge standard:

(i) For chlorine disinfection: total residual chlorine less than 100 µg/L; and

(ii) For bromine disinfection: total residual oxidant less than 25 µg/L.

(c) Additional standards applicable to discharges from pools and spas when a vessel is operating in federally-protected waters are contained in § 139.40(k).