Is this possible to have one bladder?

Yes, it is possible to have one bladder. The vast majority of people have two bladders, but some individuals are born with only one bladder. This condition is known as bladder agenesis and occurs when the bladder fails to develop properly during embryonic development. Individuals with bladder agenesis typically have other associated anomalies of the urinary tract, such as kidney agenesis (absence of one kidney) or urethral atresia (blockage of the urethra). Treatment for bladder agenesis typically involves surgical reconstruction of the urinary tract.