sewer / sower are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
sewer: (noun) a waste pipe that carries away sewage or surface water. (noun) someone who sews.
sower: (noun) someone who sows.
sewer: s·UW·er
sower: s·OW·er
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)