Legionnaires' Disease, a severe and sometimes fatal complication caused when tiny droplets of water with Legionella bacteria make it to the lungs, was diagnosed in 6,000 people in the US in 2015. Almost 600 of them died. In Arizona, the number of cases has more than doubled from 46 in 2011 to 93 in 2015, and now the CDC is reporting in its Morbidity and Mortality Weekly Report that two newborns contracted the disease in Arizona last year after home water births. Both were hospitalized and given antibiotics, and both survived. The warm water used in water births is in the "optimum range" of 77 to 108 degrees Fahrenheit for Legionella growth, per the CDC, with the Washington Post noting the bacterium can grow in storage tanks and water pipes.
Even so, the infection is extremely rare in water births, with just one other case reported in Arizona between 2011 and 2015. In 2014, a newborn in Texas died of the disease weeks after being delivered in a heated home birthing tub. In Arizona, neither infant who contracted the disease last year appears to have inhaled water during birth. One new recommendation from the CDC is to let hot water run for three minutes before filling a birthing tub "to clear the hose and pipes of stagnant water and sediment." Meanwhile, Live Science reports the American College of Obstetricians and Gynecologists says there is some evidence that early labor in water can be helpful, but due to insufficient risk data it does not yet recommend delivering babies in water. (Experts warned of the risks after the Texas baby's death.)