A holiday at the shore sounds like pure escape, but the speaker can't quite manage it. The poem opens with a comparison: the holiday is "like water in the hand." Anyone who has tried to hold water knows how it leaks away between the fingers, and here the time off seems to be draining toward the sea, the very place the speaker has come to visit. The days are already disappearing while they are still being lived.
Then the last two lines turn the mood. While the holiday runs out, the speaker's thoughts are "still running on my money." The word "running" echoes the flowing water, but this is a worried kind of motion, a mind going round and round over costs and budgets. The speaker is physically at the beach and mentally elsewhere.
The feeling is gentle, wry, and a little rueful. Nobody is in crisis, but there's a quiet sadness in seeing how worry can crowd out rest, and in noticing it only as the time slips away.