I had a look at "18th Century Collections" to check how many times "Watermill/Watermills", "Water-mill/Water-mills", "Windmill/Windmills" and "Wind-mill/Wind-mills" occurred in their wide range ofpublications. Came up with 11,135 references to wind driven mills and 7,539 references to water driven mills.
Repeated the search against 18th Century newspapers which threw up 7,580 references to wind driven mills and 2,395 references to water driven mills.
Wholly "finger in the air" (faute de mieux on my part) but, at least, consistent in identifying wind driven as the majority!!
Noticed that the Domesday Book recorded about 6,000 mills which were mainly water driven with some animal powered. Think the article mentioned "pre-windmill"? It also gave a county by county breakdown.
Best of luck with the search