The Well’s Best Friend: The One-and-Only Geotextile Filter Sock! Looking to keep your well water cleaner than a stand-up comedian’s punchline? This geotextile filter sock is the perfect sidekick. A geotextile filter sock is useful for a variety of purposes, including sediment control, erosion prevention, drainage filtration, protecting water quality in wells and stormwater management, agricultural applications, and even landscaping projects.