Answer:
I turn around once. What is out will not get in. I turn around again. What is in will not get out.
My first keeps time, my second spends time, my whole tells time.
Don't do this in the shallow end.
Autumn leaves and bad bowlers wreak havoc on this
If you drop me I'm sure to crack. But give me a smile and I'll always smile back.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.