I would like to know about journals on water resources/contamination. Is there any? I cannot afford to pay for publication, although I have some work which I believe can be published. Also, what if I'm not associated with any university, can I still publish?
Open Access (OA) is not necessarily free for authors (but free for readers). OA concerns free access to the publication. Many OA journals charge for submitting a manuscript, see for example HESS which could be an OA journal for your paper. It is possible to publish without an affiliation with a university.
Along with OA has appeared a darker side, often referred to as predatory OA journals. So choosing a journal should under any circumstances be made with care. If you are uncertain, I suggest you contact a professional at your (former) university to get some advice.