Inline water filters are generally mounted externally, most often on the wall behind or near your fridge. They are connected to your main water system and inline water filters are there to remove any toxins, heavy metals, parasites or other nasties sometimes found in tap water.
They remove impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process.
Filters clean the water to different extents for purposes such as providing agricultural irrigation, accessible drinking water.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.