What causes water buildup in the lungs?

There are many diseases and conditions that can cause pulmonary edema or fluid/water buildup in the lungs.

Starting with Infectious Diseases, any bacteria or virus that results in fulminant pneumonia will likely cause fluid accumulation in the lungs.

Acquired diseases such as cardiovascular disease often cause pulmonary edema through impaired blood return to the heart.

Cancer can also cause pulmonary edema, both through inciting an inflammatory response as well as mechanically blocking adequate blood flow.