Membranes are used to filter out contaminants and unwanted substances from groundwater, industrial water, seawater, brackish water and other sources. Different membrane types and sizes can be used depending on the application, including ultrafiltration (UF), reverse osmosis (RO), nanofiltration (NF), microfiltration (MF) and forward osmosis (FO). With the ability to filter out much smaller substances, including salts and ions from liquids, membranes have become popular and commonplace in water treatment configurations. Membranes manufactured from polymer films are the most common, with other materials such as ceramics also starting to gain traction. Research into newer materials including graphene and carbon nanotubes is also underway.