I am amazed how little grasp you seem to have on the whole situation.
1) is the water tower your property?
2) is the water tower even connected to your property?
3) are they actually proposing to install additional antennas on your property?
If you answer no to all of the above why were you even asking the question in the first place? What does it have to do with you?
The reason they would have told you that you would be able to upgrade is because if the water tower base station was installed they would be able to re-location your antenna to connect to that. You would then only need a small (short distance) antenna and would likely see a very real boots in speed, unless you are already rate limited down to the service level you are paying for.
Even with a base station on the water tower you (your property) would not be a 'repeater'.
3 poles likely means they plan to have 3 sector antennas. Going by the fact that these are all one side I expect they are only planning 180 degree coverage using 3 x 60 degree antennas. Which if there is a hill or no properties behind this would make sense
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