Can somebody enlighten me as to why the native tribes are considered a large user of water? The article mentions them as a part of this agreement a few times, b

Can somebody enlighten me as to why the native tribes are considered a large user of water? The article mentions them as a part of this agreement a few times, but not why they would have a more significant impact on the water use than any other town or city (assuming when they say tribes they mean the reservations). Perhaps that's not how it works in the US? Or are they saying agriculture by the native tribes, and therefore that is considered different from non-tribe agriculture?