Does it really matter on what you feed your horse? Because I noticed that most of the people feed their horses hay and water.. Is that their diet? Becuase if I do get a horse that'll be what I feed it becuse of how many people use those two things.

Most people feed their horses a pelleted grain as well as hay and water. There are different types of grain, kind of like how there are different types of Dog chow. There are foal, regular, performance, senior, etc. When/if you buy a horse the current owner should tell you what they use and how much and when. You can then decide if you want to feed at a different time, or a different brand. One of the new products last I was riding was a food called Dengie which had all the hay and grain in a cube. So you just fed then Dengie and water to make life easier. Of course it cost a bit more than just grain, but its easier to get than hay in some areas.

I think what a horse is being fed depends largely on what kind of work it's doing, how good (or not good for that matter) the grazing is that is available. There are also some special requirements if a horse is prone to laminitis, gains weight easily or has other health issues.

I help out with caring for 12 horses and a donkey. Some of them aren't ridden at all (retired/have health-problems that rule out ridden work), the others are ridden a couple of times a week.
Because of that most of them are fed hay and straw and have unlimited grazing over night and a mineral lick-it thingy. There is no need for grain or any extra food. Some of them could actually lose a couple of pounds ;)

We have a little group that have had laminitis and are therefor kept on a sand paddock with hay only. Our "senior" (34 years old) is fed a mash-like senior-pellets mix with water several times a day, since his teeth are too worn down to eat hay properly.
Another horse has been severely neglected and almost starved to death before it came to us. It is also fed on hay and grass only and is slowly but steadily gaining weight on it's way to being a healthy horse again.

As purplefdu said said, feeding a ready-made grain/pellets mix does save time. Just make sure to get the right kind and amount for your horse. Most feed-suppliers (at least in the UK) have hotlins that you can call to get info about the different types they carry.

Also your vet might be able to help with picking out the right food.
Always remember though to introduce food changes slowly so you won't upset your horses digestive system.

Mefiant

I asked my vet this same question. His answer was good quality grass hay and clean water. He wasn't a believer in feeding extra grains to a horse. I have to agree with the other posters that it depends on what you're doing with the horse and the horses age. I actually feed a rice bran (my horses love it) for two reasons. 1) it contains extra vitamins and makes their coat shine, but 2) I can sneak stuff into their feed. For example we have a problem with sand in the horses gut so I sneak in Sand Clear. They wouldn't touch Sand Clear alone, but with the rice bran they eat it.

I think the original diet of horses is grass and that is the best food to feed them. My father and I usually cut fresh tall grasses near the forest for the food at night. At day, we guide them through a good pasture for feeding.

Does it really matter on what you feed your horse? Because I noticed that most of the people feed their horses hay and water.. Is that their diet? Becuase if I do get a horse that'll be what I feed it becuse of how many people use those two things.

its good to look back to remember this early stuff.

So I take it when you are giving a horse a treat its just that a treat not an essential part of their diet, or is that incorrect? I have been told both but would love some clarification.

I have always been told that they need grains based on activity level. If you work them, they need the added nutrients to suppliment the hay. In normal circumstances the horse will spend the day grazing so only needs the calories and nutrients consumed with hay and grass.

It would depend on the nutrition of the "treat". If you're giving your horse carrots and apples its different than sugar cubes and commercially prepared treats with sugar, molasses, etc. If there is a high sugar or grain content it should probably be counted as part of their diet, just like with dogs. If you give tons of treats cut back hay/grain portions accordingly.