Pulmonary edema, which is an abnormal buildup of fluid in the lungs, can be caused by various factors. The most common cause is congestive heart failure, where the heart is unable to pump blood effectively, leading to fluid backup in the lungs. Other causes of pulmonary edema include pneumonia, exposure to certain toxins, medications, trauma to the chest wall, and traveling to or exercising at high elevations. Additionally, conditions such as acute respiratory distress syndrome (ARDS), drug reactions or overdose, smoke inhalation, and immersion pulmonary edema can also lead to the accumulation of fluid in the lungs. Its important to note that pulmonary edema can be categorized as either cardiogenic, where a heart problem causes the fluid buildup, or noncardiogenic, where the cause is not related to the heart.

In summary, water in the lungs, or pulmonary edema, can be caused by a variety of factors, including heart problems, pneumonia, exposure to toxins, medications, trauma, and high elevations, among others. Understanding the underlying cause is crucial for appropriate diagnosis and treatment.