肚子里有墨水 (literally 'has ink in the belly') is an idiom meaning someone is well-educated or knowledgeable. 没有墨水 means uneducated.
history
墨 originally referred to ink sticks used in Chinese calligraphy. 文房四宝 (wénfáng sì bǎo, Four Treasures of the Study): 笔墨纸砚 (brush, ink, paper, inkstone).
