The water intrusion volume is the volume of water that penetrates (intrudes) into the structure of a hydrophobic membrane at a given applied pressure (typically held for 10 minutes). The water intrusion test (WIT) or water flow test (WFT) has been designed to eradicate the need for solvent wetting with a ‘contaminant’ such as IPA (isopropyl alcohol) or ethanol to integrity test hydrophobic PTFE membrane filters. Other liquid based tests for hydrophobic PTFE membrane filters require the membrane to be wet out with a solvent prior to testing. The use of IPA, especially if attempting to test multi-round systems can also pose a health and safety issue due to flammability. The water intrusion test method measures the dry membrane’s resistance to wetting with DI /WFI grade water during an applied gas pressure.