A style guide lays out how you will treat elements of writing when they appear. It can cover things like when to capitalize, when to abbreviate, how to refer to something on a second reference, whether to use a numeral or spell out a number, whether something should be italicized or put in quotes, and more.
There are various style guides available to use – such as the AP Stylebook or Chicago Manual of Style – that detail out how to style just about anything when it comes to words and punctuation. You don’t have to get into everything, but you may want to be consistent on a few basics such as when to use numerals or numbers and how you will treat specific words relevant to your utility or city such as how to refer to something on the second reference. Not everyone in an organization will be consistent so when it comes to public communications, you might want to consider making someone the point person to review everything before it’s distributed externally.