Water dilutes the glue, making it less effective. To get glue to the bottom of a crack you need to open it up, i usually drive a knife/flathead screwdriver or similar into the crack to open it slightly and then get glue into the crack using needles. Printers ink needles are on ebay and work very well. From there it would be a case of using parcel tape, or cut up grips to hold the crack closed. There are some cases that would require a clamp, this isn't one of them.
This crack is so minor i might even be tempted to sand it out, and it is so close to the surface that i wouldn't advise opening it up.
My advice would be to get a really runny superglue, dribble it into the crack, let gravity take its course for a few seconds and then squeeze the crack shut with your hands and hold for a minute or so. Applying shoe goo or a toe guard afterwards finishes the job perfectly.