how to measure time with a tin can containing water
Some ideas:
1. punch a hole at the bottom and see how long it takes to drain. Note that the height of water remaining is not proportional to elapsed time.
2. For long periods, see how long it takes for water to dry out. This is of low precision because the evaporation time depends on humidity and air movements.
3. Fill the can with a dripping faucet. The height of water is almost proportional to the elapsed time. Evaporation must be considered if long periods of time are measured.