Two highs and two lows, and never at the same time
The tide is the sea rising and falling because the moon, and to a lesser extent the sun, pull on the water as the earth turns. Around Britain that gives two high waters and two low waters in a tidal day of about 24 hours and 50 minutes, which is why each day's high water arrives about an hour later than the day before. How much later varies from day to day — you can see it in the table above.
What the heights mean
The figures are heights of the water above chart datum, a fixed low-water mark worked out separately for each port — Blackpool and Fleetwood each have their own. So 7 m does not mean the water is 7 m deep. It means the surface is 7 m above that mark. For anything on the beach, the number that matters is the difference between the high and the low: the wider the gap, the further the water has to travel and the faster it covers the sand.
Springs and neaps
The tide does not run at the same size all month. Twice a month it reaches its biggest, just after a new moon or a full moon, when the sun and the moon are lined up and pulling the same way; these are spring tides. Twice a month it is at its smallest, when the moon is at right angles and the two pulls partly cancel out; these are neap tides. Over the seven days above, the gap between high and low water at Blackpool runs from 2.8 m to 7.8 m (widest Sun 25 Oct).