There seems to be a bit of a discrepancy in the car washing sector as to where the carwashes the term "carwash" or "car wash" is most appropriate, that is to say or is it two-words. Okay so, since, I've been in the industry myself for nearly 30-years prior to retirement, I'd like to discuss this with you for a moment, and give you my take on this controversy.
Interestingly enough, the term "Carwash" has been used since the industry started, but many people use "car wash" online, and when they talk, so over the years, it seems to be either / or both. Unfortunately, using "car wash" also confuses those who are adamant about proper English, because it confuses the noun with the action to wash a car.
Neverheless, I can say this, I was instrumental in my career of modifying the English Language to use the term "car wash" as a verb and as a noun, and looking back, I rather like it that way. Now then, during most of my career I was on the mobile side of the industry.
No one in the mobile car washing industry uses the word "carwash" to describe their businesses, and most everyone in the traditional location based carwashes uses "carwash" to describe their operations. That's why I used the term way I did, although I bet you could find a half a dozen English Majors or professors in any given school who would not agree with my take on this or the realities of a changing and evolving industry.
So, that's why I think I may disagree with English Teachers, I've changed the term over the years, and I like my way better, even if you search the word online the search engines seem to pull up businesses, and does not Seem to pull up very many car washing "action" type websites. The world has changed, so it's time that all editors, English teachers, and public get used to it, and change or get run over by the onslaught of actual users of the language, and look out now, because here comes China with more English speaking folks as a second language than the number of people in the US. India is next, so we are all going to have to deal with that.
When reading about this word in Wikipedia, it immediately announces that both uses of the word are common, and seems to indicate either are perfectly acceptable. I tend to agree with that, and would submit to you that when considering mobile businesses, you always should use two-words to describe it, and when talking about a fixed site location, you should generally or mostly use the one-worded version, Which most in the industry would agree. Indeed, I hope this clears things up for you, please consider all this and think on it.