Rama Rao, the protagonist, utilized his sizeable inheritance to invest in the gramophone company and became an agent of Malgudi. His fortune seemed secure until the crash of the stock market coupled with the death of a Bombay financier. The economic struggles eventually made their way down to Rao. As he struggled to keep his family accustomed to the life of relative ease, "the money in the bank was fast melting". This references the heavy financial demands on the savings. The balance melted, or dwindled, quickly just like an ice cube will when subjected to heat or pressure.
Narayan uses the clever metaphor to paint a picture of the savings. Rather than a gradual depletion, the reader can envision the numbers tumbling down each day. For anyone who has faced difficult times, the emotional connection to Rao is cemented with the shared frustration of lost savings.