Why does different samples of water have different pH values? Please I need to know right away.

The request of question is vague since it does not specify if the source of samples of water is the same or it changes with each sample collected.

The pH of samples of water can vary even if the source remains unchanged, because the pH of water can fluctuate over a 24 hours cycle because of the process of photosynthesis of aquatic plants. During night, the pH decreases because the aquatic plants release the CO_2 in water, in the process of respiration. There exists also seasonal fluctuations of pH in summer time than winter time because, in summer, the increasing of temperatures and light generate higher respiration rates of aquatic plants.

If the samples of water are collected from various sources, then there exists a great number of factors that can produce fluctuations in pH of water.