It's difficult to tell anything from photograph of a chicken lying dead. Since this is the second death I would urge you to send it off for a necropsy.
It may just be the angle of the photograph but your chickens appear to be overcrowded. That will cause stress and stress can lead to illness. For that many chickens, at least 2 food and water stations would be a very good idea. The waterer you have should be fine. If it is adjustable I would suggest you have it set to completely fill the saucer because that many chickens will need plenty of water, but you really need another one in case one gets knocked and spilt. Water is crucial to chickens, particularly in the summer. It helps them to cool down. I would also hang that waterer higher so that it is just below head height. That will keep it cleaner and reduce the chance of it being tipped and spilt as well as giving the chickens a little more space.