i have a mare that is due to foal in about 3 weeks i have notice the last few days her water tank is not getting any lower. what would make her not drink very much?? same tank, same hose, same water. i can't see anything forgien in the tank. i know she has been drinking some because her feed bucket had rain water in it and she drank some. i have put out a bucket with water and today i put out another tank in the other pasture.