Dear- thanks for using our service .Dark urine that improves after drinking a lot of water most likely was secondary to concentrated urine due to dehydration . Other possibilities are occult blood from any kidney stone,urinary tract infection or cystitis. However, those conditions don t improve so fast with just water. I think that this situation was secondary to dehydration mostly because you had alcohol intake the night before and that can cause increased urinary output and dehydration. I hope that my advise has been helpful DR.JC