Water bill is 400% higher then last bill, faulty meter or leaks?

[Henry Lazerow]

I have a 4 unit in Rogers Park that received a water bill over 400% higher then last billing period. The building has been fully occupied with same tenants all year so I do not see any actual increase in usage. Is this likely from a leak or a faulty meter? What's best course of action disputing the bill or areas I should check for leaks? 

Thank you,