The visitors are alarmed that Mr. Jones isn't given a glass of water immediately. As much as the nurse may understand their concerns, they may not explain what is actually transpiring. They cannot breach that confidentiality to explain how excess fluid can be harmful to his health, in light of his renal problems. Nurses understand this because they know situations on the surface can appear a certain way. When appropriate and able, they combat the phenomenon with education.
Nurses know first hand, education decreases anxiety.