The student should make sure that the instrument she will be using to measure the pH of the water is valid.
Validity is concerned with an object's goal is able to measure the intended object.
With this conclusion validity, our data gathered and presented are considered a reasonable one. It is the most important types of validity. As what is said, by having conclusion validity, your data will be undoubtedly least considered since it is labelled as statistical and well-studied. Once you already mention the word statistics meaning it is studied and surveyed with the most of the human race and includes relationship in your data.