A pressure gauge may not seem like a valuable tool for a reverse osmosis water filtration unit, but they are in fact quite critical. Not only will a pressure gauge tell you if your RO unit is running at the optimal pressure, but it will also tell you when pre-filters need to be replaced. An RO unit with a good supply source of water runs at about 75-90 psi or more. However, if a filter gets clogged, that number can drop to half or less. The blockage in the filter restricts water from passing through easily, causing a lack of water flow and a dramatic drop in pressure. This causes the entire unit to operate less efficiently. This could mean the water trickling out could do so more slowly, or the membrane itself could become damaged or degrade faster.