Semi-Aqueous Cleaners are a group of cleaning solutions composed of natural or synthetic organic solvents, surfactants, rust inhibitors and other additives. The term semi-aqueous refers to the use of water in some part of the cleaning process, such as washing, rinsing, or both. In general, they have a good ability to remove heavy grease, waxes and tar. Their low surface tension allows them to penetrate small spaces. Some also have low vapor pressure and thus have low volatile organic compound (VOC) emissions. Depending on the type of cleaner, adverse effects will vary; some may be toxic to aquatic life, others are highly flammable or need rinsing and drying.