The phrase "a waste of three years" is correct and usable in written English.
You can use it when expressing that a period of three years was not productive or beneficial in some way.
Example: "After reflecting on my time at that job, I realized it was truly a waste of three years."
Alternatives: "a squandered three years" or "a loss of three years".
I regret terribly the stress it put on my mother and family – it was such a waste of two years of my life.
It was a waste of four years that we could have spent making TV shows that would have been way more fun.
I think what a waste of time, four years at that place, me a little Heeb from Hartford, but last November I had to be in Hollywood when the Yale-Harvard game was played, and God damn it if I don't have a special wire with the play by play.
But there is an even better prospect for easing the future burden: the development of so-called fast reactors capable of reducing the lifetime of radioactive waste to a couple of hundred years.
"It would be a shame to waste the work of two years.
At that moment, the bitter taste not just of a single defeat but of four years of wasted effort can simply be too much for some to handle.
While George R. R. Martin and the show creators Weiss and Benioff are perfectly willing to kill off major characters, it just seems like a waste to blow five years of foreshadowing without giving us the revelation (and then killing him off, no doubt).
People are shifting their consumption habits, with leaders like Lauren Singer helping others to live a lifestyle of zero waste – two years of Lauren's trash fits inside a single mason jar.
It estimates an average cost saving of between £5,500-£6,000 per business, with an average cut in food waste of five tonnes a year – the weight of three London taxis.
A US government report from 2011 concluded that monetisation resulted in the waste of $219m£139m9m) over three years.
