Which of the following statements is true regarding surface water?

The statement that bacteria, algae, and turbidity can be problematic in surface water is true. Surface water sources, such as rivers, lakes, and reservoirs, are subject to various natural and anthropogenic influences that can lead to the presence of bacteria and algae. These microorganisms can thrive in nutrient-rich environments, often exacerbated by runoff from agricultural and urban areas, leading to issues like harmful algal blooms. Additionally, turbidity, which measures the cloudiness of water due to suspended particles, can affect water quality by blocking sunlight necessary for aquatic plants and disrupting the aquatic habitat. Elevated turbidity can also indicate the presence of pathogens and other contaminants, making it a crucial factor in assessing surface water quality.

The other statements focus on misconceptions or overly narrow assertions. Bacteria and algae are naturally present in many water bodies, meaning their absence is not a realistic scenario. Concerns regarding water quality aren't limited to just agricultural pollution, as urban runoff, industrial discharges, and other sources can also introduce pollutants. Lastly, municipal water treatment processes aim for purity, but it is not guaranteed that municipal sources are always free from contaminants, particularly without adequate treatment and monitoring.