From: Daily Writing Tips
A convention of English spelling is that the letter q is followed by the letter u.
Very few English words omit the u after q. The most common that come to mind are foreign place names like Iraq and Qatar, and made-up words like qwerty, Nasdaq, Compaq and Qantas.
In borrowings from languages in which the native q represents a sound unlike the sounds represented by English q, the q is usually anglicized to a k or a c: Qaballah>Cabbala; Quran>Koran; faqir>fakir.The most frequent pronunciation of qu is [kw], as in queen: acquire, acquit, aquatic, aqueous, aquifer, banquet, bequest. Enquire, equal, equine, equinox or esquire.
The second most frequent pronunciation of qu is [k], is found (mostly) in French borrowings: antique,
barque, bisque, bouquet, briquette, clique, conquer, croquet, lacquer, liqueur or liquor.
The Spanish borrowing quinoa appeared in English as early as 1598, spelled quinua. The earliest example in the OED of the spelling quinoa is dated 1758. Quinoa is a plant related to spinach. It enjoys popularity among the health-conscious because of its high protein content and lack of gluten. The OED lists four pronunciations, two British and two American. I’ve heard it pronounced KEEN-wah, KIN-wah, and Kwi-NO-ah. Those in the know call it KEEN-wah.