Cat Dandruff - Tumblr Posts

Hi i know this isnt quora but does anyone know why my cat has dandruff?

I think it could be dehydration, anxiety or food allergies. He's been having it for a long time know and it bothers me because he is itchy and has dry skin. I dont really have the money to go to the vet since thus is considered a trivial matter but i still care a lot for him. I suspect dehydration and food allergy because my cat is very strange when it comes to food, he refuses to eat anything that isn't kibble even treats like churu or wet food. He seems to be dehydrated because his poop tends to be dry and he usually has a hard time going to the litter plus he is extremely clumsy and doesnt know how to drink anything. We have tried fountains and they have worked a little but he still drinks out of his paws and drops the water everywhere. He also has really dry and itchy skin on his back and is very sensitive when touched anywhere near his column plus he sometimes gets irritation because he bites himself while grooming his back. I dont know if it's anxiety because he does have separation issues and tends to cry a loooooot but it would really calm me down if a vet told me it's just normal. Also he is an orange english shorthair so no hereditary sebhorrea from siameses.