The drug your husband was given, Myrin P-Forte is a combination drug used for the treatment of tuberculosis. It contains 4 different anti-tuberculosis drugs (Ethambutol+Rifampicin+Isoniasad+Pyrazinamide). These are all good drugs for the treatment of TB.
The “water in his lungs” was probably what is called a pleural effusion; that is, a collection of fluid around the lung. In parts of the world where pulmonary (lung) tuberculosis is common, the development of fluid secondary to the TB is also common. So, the doctor might have treated your husband for the correct disease. It is possible that the fluid went away on its own and had nothing to do with the Myrin P-Forte, but that is less likely. But, if the treatment did cause the TB to go away, it is quite possible that the TB has returned and that he now again has fluid on or in his lung.
The first step is for the doctor to find out why your husband is “hard in breathing again.” If it is because of “his lung full of water”, the fluid should be removed and, if possible, sent to the laboratory and examined to see what most likely caused it. The fluid should be cultured for TB. In the meantime, while waiting for results of the fluid exam, the treatment for TB should likely be started again, to get a head start. But remember, there are many causes of water on the lung and you should depend on his doctor to discover and treat the cause.