Email has become a staple of business communication and although it's essentially free it has a hidden cost in terms the time spent dealing with it.

Collaborative email service Contatta has released an infographic which quantifies how time consuming and costly business email has become.

According to its figures the average worker spends 13 hours of their working week reading and answering email, which equates to an estimated 637 hours annually. Assuming a median professional wage of $23 per hour, that means businesses pay over $15K per employee to use email. Looked at across North America that means employees spend nearly 75 billion hours on email, costing businesses nearly $2 trillion in salaries -- that's almost 14-times the combined wealth of Bill Gates, Oprah and Warren Buffett.

More comparisons to show what that cost really means are in the infographic below. If you want to try to claw back a few of those lost dollars you can get a 60-day free trial of Contatta's collaborative solution, which aims to help employees use email more effectively, on the company's website.