What causes year old gelding to drink excessive amounts of water eat a lot of salt eat good pee a lot ribs show and is wormed regular?

Well first off if the horse is acting strange or is not putting on weight then you should contact and equine vet immediately. Now a yearling gelding should be healthy and not behaving oddly at all. The horse would be drinking excessive amounts of water due to the large amounts of salt it is ingesting, the most likely cause for this is the summer heat, horses will drink more when it's hot outside.The large amounts of pee would be due to the increase intake of water. You say the horse is dewormed regularly, but you should have a fecal egg count done to ensure that the product you are using is effective. You also say the horse eats 'good', but what exactly is it eating and how much? The horse should be getting between 1% to 3% of it's bodyweight in food daily. The horse should not be 'ribby', have the vet check the horse thoroughly for parasites, dental issues and have a blood panel done to exclude illness.