The Environment Agency announced the change on Friday 9 October, after months of unusually dry conditions left rivers, reservoirs and the wider environment with unusually low water levels.
Yorkshire had already been classed as being in prolonged dry weather following a lack of rainfall during spring and summer.
The Environment Agency says recent rain has not been enough to reverse the deficit.
People are being encouraged to use water carefully, avoid unnecessary water use and help reduce pressure on supplies.
Yorkshire Water says it is continuing to monitor the situation.
At present there has been no announcement of new customer restrictions specifically because of today's drought declaration.
Source information
Source: Environment Agency, Yorkshire Water