Noah Joad is Ma and Pa Joad's oldest son. He "left the impression of being misshapen, his head or his body or his legs or his mind; but no misshapen member could be recalled" (9.87). Pa Joad was terrified when his wife went into labor with their first child. They were alone in their house, and so Pa had to deliver the baby.
He did so with his hands, pulling the baby out. When the midwife finally arrived, she had to mold the baby's body back into shape. Ever since then, Pa Joad has lived with major guilt about his son, and so he is warmer to Noah than he is to any of his other children.
When the Joads reach California and stop to camp by the Colorado River, Noah falls in love with the cool, clear water. He decides right there and then to live by the river forevermore. He decides not to follow his family any further. When Tom tries to convince him to come with the family, Noah replies, "You know how the folks are nice to me. But they don't really care for me" (18.114). Ugh. That's heartbreaking.
When Tom tries to talk sense into him, Noah says,
"It ain't no use. I was in that there water. An' I ain't a-gonna leave her. I'm a-gonna go now, Tom—down the river. I'll catch fish an' stuff, but I can't leave her. I can't." (18.116)
Noah finds something in the Colorado River's waters that he can't part with for all the world.