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We present Herschel/HIFI observations of the fundamental rotationaltransitions of ortho- and para-H$_2^{16}$O and H$_2^{18}$O in absorptiontowards Sagittarius~B2(M) and W31C. The ortho/para ratio in water in theforeground clouds on the line of sight towards these bright continuum sourcesis generally consistent with the statistical high-temperature ratio of 3,within the observational uncertainties. However, somewhat unexpectedly, wederive a low ortho/para ratio of $2.35 \pm 0.35$, corresponding to a spintemperature of $\sim$27~K, towards Sagittarius~B2(M) at velocities of theexpanding molecular ring. Water molecules in this region appear to have formedwith, or relaxed to, an ortho/para ratio close to the value corresponding tothe local temperature of the gas and dust.

Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C