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By: Joe Czaszynski

Determining the cause of an interior leak at a large commercial or multi-family residential building can be difficult. Certain methods can help decipher the source or sources of water infiltration. Water testing at and around the exterior of suspected infiltration locations is one of the most helpful, and least invasive methods.

A water test can simulate the conditions of a rain event, can be precisely aimed at a suspected leak location, and in many cases, can recreate the conditions experienced by the resident. By narrowing down the cause of water infiltration, the design professional can recommend the proper repairs, rather than a broad scope of work to address several areas that may not be sources of leaks.

Different methods and materials can be used to perform a water test. Typically, some form of spraying apparatus is used. A spray bar or rack has multiple spray nozzles and a pressure gauge that measures the flow of water. It’s an excellent way to apply water to a large section of an exterior wall, window(s) or door(s). A single spray nozzle is used to focus on small areas, such as portions of flashing elements on windows, doors, or façades. It can also be directed upwards, or at elements that are harder to access. A common garden hose without any attached nozzle can saturate or flood a particular area, and can be used to cascade water over a suspected area. Unlike the spray bar or spray nozzle, the hose without a nozzle cannot accurately simulate a rain event, nor can it measure water pressure like a spray bar or a single nozzle with a gauge attachment.

A spray rack is typically positioned in the general area of the suspected water infiltration. Arms on the rack can position it away from the exterior testing area to allow for better overall coverage. Water is then applied for a duration representative of the conditions observed during leaks, during which time, interior observations are made. If any leaks are detected, the water is turned off and the test is concluded. If no water infiltration is observed during the test, the water is turned off for a significant period of time, often the same duration as the test, dependent on several factors, including the construction of the building elements. This allows the recently sprayed water a chance to naturally flow and settle, the way it would after a rain event. If no water infiltration is observed the same test may resume or separate tests at other potential sources of water infiltration may be performed.

Other tools are often employed before, during and after water tests. A moisture meter can measure the moisture content of interior walls, ceilings and trim. An infrared camera can also be used at the interior leak location to detect temperature changes that occur within the walls. This change in temperature often reflects the path of water infiltration. These tools, along with water testing methods, can often circumvent the need for more costly and invasive investigation. Since much of the test described above is subjective, the experience and practical knowledge of the expert performing the water test is often the most important variable in the outcome.


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Sullivan Engineering provides high-quality building envelope restoration and compliance solutions.

We partner with facilities managers and account executives to provide technical expertise and project management for building envelope restoration, compliance, and maintenance.

Our solutions reduce the overall building life cycle maintenance costs by creating long-lasting, high-quality work for years to come.