Which of the following sampling techniques involves collecting multiple small samples at different times?

Composite sampling is the correct choice because it refers to the process of collecting multiple small samples at different times and then combining them into a single sample for analysis. This technique allows for a more representative assessment of a larger area or time period, as it averages out variations that might occur from one sample to another. This is particularly useful in water distribution where conditions can change due to various factors such as time of day, weather conditions, or usage patterns.

In contrast, grab sampling involves taking a single sample at a specific time, which does not account for variations over time. Random sampling also refers to choosing samples in a way that gives all parts of the area an equal chance of selection, but it does not explicitly involve multiple samples over different times. Incremental sampling, while it may sound similar, actually refers to a process where samples are taken in predefined increments rather than collecting multiple small samples over different times.