Which of the following is a method for testing water quality?

Testing water quality is crucial for ensuring that water is safe for consumption and ecological health. Colony count, which refers to measuring the number of bacterial colonies present in a water sample, provides insights into the microbiological quality of the water. This method is important for detecting harmful pathogens that could pose health risks to people and wildlife.

The SPADNS test is a specific chemical test used to determine the concentration of fluoride in water samples. This test helps in assessing compliance with health standards and understanding the fluoride levels' impact on both human health and environmental safety.

Both of these methods (colony count and SPADNS test) are valid approaches for analyzing different aspects of water quality. Visual inspection, while it can provide preliminary observations about clarity or obvious contamination, does not yield quantitative or confirmatory data about the water's safety or chemical parameters. Hence, it does not serve as a reliable standalone method for assessing water quality.