To these human costs can be added the massive economic waste associated with the water and sanitation deficit.… The costs associated with health spending, productivity losses and labour diversions … are greatest in some of the poorest countries. Sub-Saharan Africa loses about 5% of GDP, or some $28.4 billion annually, a figure that exceeds total aid flows and debt relief to the region in 2003.Source 10
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.