Usage of Indefinite Article

Question

I am wondering whether both of the following sentences are acceptable:

(A) Only water bottles with "caps" are allowed in this area. (B) Only water bottles with "a" cap are allowed in this area.

If I want to emphasize the importance of having A CAP on the bottles brought into the area, would it be acceptable to put "A" instead of "CAPS"?

Please advise.

Thank you

Answer 1

(A) seems better than (B) - keeping the plurals consistent.

Honestly I'd prefer other approaches:

1. Please no open water bottles here
2. No open water bottles are allowed in this area
3. Only closed water bottles are allowed in this area
4. Cap your water bottles please

Answer 2

Emphasizing the importance of having something is best done by the definite prohibition of not having it. The indefinite article (by its very definition) is unsuited to this concept :

Capless water bottles are prohibited in this area.

Or :

Uncapped water bottles are prohibited in this area.