  Of the many recently discovered terrestrial exoplanets, some are expected to
harbor moderate water mass fractions of a few percent. The formation pathways
that can produce planets with these water mass fractions are not fully
understood. Here, we use the code chemcomp, which consists of a semi-analytical
1D protoplanetary disk model harboring a migrating and accreting planet, to
model the growth and composition of planets with moderate water mass fractions
by pebble accretion in a protoplanetary disk around a TRAPPIST-1 analog star.
This star is accompanied by seven terrestrial planets, of which the outer four
planets likely contain water mass fractions of between 1\% and 10\%. We adopt a
published model that considers the evaporation of pebbles in the planetary
envelope, from where recycling flows can transport the volatile vapor back into
the disk. We find that with this model, the planetary water content depends on
the influx rate of pebbles onto the planet. A decreasing pebble influx with
time reduces the envelope temperature and consequently allows the formation of
planets with moderate water mass fractions as inferred for the outer TRAPPIST-1
planets for a number of different simulation configurations. This is further
evidence that the recycling of vapor is an important component of planet
formation needed to explain the vast and diverse population of exoplanets.
