One foot swollen 2 weeks

[LilyLabVA]

In my efforts NOT to google I was wondering if anyone can tell me if I should be concerned about the fact that my left foot becomes slightly puffy off and on for about 2 weeks? I wear flats to work. Its not very noticiable to others unless you are looking for it. However my good friend actually pointed out to me that the top of my foot appeared puffy.
Any normal, benign things this could be?

[nomorepanic]

water retention. Loads of things non sinister

[LilyLabVA]

Thank you both! Sorry but again, trying not to google.... what exactly is water retention and how can I sort it out? Would it occure in just one foot?