Ashok had a garden in his house and he took real good care of the plants in his garden. It so happened that he couldn't really look after his plants for a few days because of incessant rains in his place. When he finally went to check up on his plants, he noticed that instead of growing up, they had drooped and the leaves had turned pale green. He also observed that the lustrous white marble pillars of his house had lost its shine and turned yellowish. He collected the water sample when it rained again and found that blue litmus paper turned red upon exposing it to the collected water.
What could be the possible reasons for his observations?