Aqueous composition having improved hydrophilic drug penetrability

Provided is an aqueous composition containing a hydrophilic drug, wherein in order to improve the penetrability of the drug into the site of action of the drug so that a desired effect is exhibited at a low dose and safety when using the drug is improved, the aqueous composition contains the hydrophilic drug and a benzalkonium halide and has an osmotic pressure ratio of 0.5 or less. The aqueous composition preferably further contains a polyhydric alcohol. Further, the benzalkonium halide is preferably benzalkonium chloride.