It was the second day of turbulent weather in the state, where at least three people died in floods in central Texas on Friday. Another person is still missing in the Austin area.
The storms and suspected tornadoes, which forecasters say were caused by an upper-level disturbance from Mexico, hit an already-sodden swathe of Texas that was still drying out from the remnants of Hurricane Patricia.
The eight members of the church group were at a lazy creek cutting through Texas wine country, a popular getaway spot, when it swelled into a rushing torrent.
They had to escape to the second floor before the National Guard arrived to rescue them.
In the Houston area, up to 8in (20cm) of rain fell since Friday night, though it had mostly stopped by early Saturday afternoon. The water, however, flooded streets and freeway frontage roads and caused bayous to spill over their banks.
The Houston Fire Department said it had responded to more than 130 water rescues by mid-morning on Saturday, and some public light-rail and bus transportation was suspended.
Houston officials also said they had received 44 reports of structural flooding, including homes and businesses, and the city's fire department helped remove residents from flooded homes near a bayou in the north-eastern part of the city.
Houston police discovered the two bodies that are believed to be weather-related deaths, one in a flooded ditch and another in a wooded area where there had been high water, according to city spokesman Michael Walter.