You don't necessarily need to put the mineral or bait near the water. Deer will utilize each one at seperate times, and by not placing them all in one spot, you will encourage deer to utilize more of your land rather than concentrate all their activities at one location. When their activities become too concentrated, they will overutilize the forage in that area, while forage in other areas is underutilized.

To get a true estimate of the population, you really can't rely on data obtained at points of concentration.