Abdominal X-rays should not be used to check for ascites. If this diagnosis is suspected then again ultrasound is the best initial investigation, and can also be used to assist drainage.
Fluid and soft tissues have similar densities, and so ascites may be mistaken for organomegaly. The bowel does not appear pushed to the side as in organomegaly, but rather gas filled bowel rises in a central position, in the supine patient.