"The following day more water is added."
Translation:Il giorno seguente si aggiunge più acqua.
Think of it as if you were reading instructions or a record of events. It may tell you after one things is done, what is done the "next day", or in this case "the following day." I hope that gets at your question. A better way to write it might be with a comma after "day" (or after "seguente" in Italian).