Up to about half a metre of water submerged two housing estates in Lak Si district, about 15 kilometres from the city centre, the district's chief engineer Pramin Kosumphan told AFP.
"There are more than 1,000 households in each housing estate," he said. "The water overflowed from the Prapa canal but it's stable now and residents were warned in advance."
Bangkok residents were advised to move their possessions to higher floors or safe areas as the capital braced for the arrival of the floods from the central plains, which are several metres under water in places.
Three months of heavy monsoon rains have killed at least 342 people in Thailand and damaged the homes and livelihoods of millions of others, mostly in the north and centre.