| Acid | Molecular substance or other chemical that releases hydrogen ions (H+) in aqueous solution |
| Adsorbs | Attracts and holds on its surface (charcoal, for example) |
| Aeration | Mixing of air into a liquid; as in water flowing over a dam, or in sewage treatment |
| Aerobic bacteria | Oxygen-consuming bacteria |
| Anaerobic bacteria | Bacteria that do not require oxygen to live |
| Anion | Ion possessing a negative charge |
| Aquifer | Porous rock structures which holds water beneath the earth’s surface |
| Atom | Smallest particles possessing the properties of an element; all matter is composed of atoms |
| Base | Chemical that yields hydroxide ions (OH-) in aqueous solution |
| Biodegradable | Able to be broken down into simpler substances by bacteria |
| Cation | Ion possessing a positive charge |
| Chemical bond | Force that holds atoms or ions together in chemical compounds |
| Chemical change | Change in matter resulting in a change in the identity of one or more substances. Indicated by change in color, production of heat or light, creation of precipitate or gas |
| Chemical compound | substance composed of two or more elements that cannot be separated by physical means |
| Chemical equation | Combination of chemical formulas that represent what occurs in a chemical reaction |
| Chemical formula | Combination of symbols that represents the elements present in a substance with subscripts showing the number of atoms of each element |
| Chemical property | Property of a substance related to a chemical change undergone by the substance |
| Chemical reaction | Change in matter in which one or more chemicals are transformed into new or different chemicals |
| Chemical symbol | A one- or two- letter expression that represents an element; the symbol Na represents sodium |
| Chlorination | Treatment of water with chlorine, for disinfection |
| Colloid | Mixture containing large particles that are small enough to remain suspended (don’t settle) |
| Compound | Substance composed of two or more elements that cannot be separated by physical means |
| Concentration | Quantity of solute dissolved in a specific quantity of solvent or solution |
| Condensation | Conversion of a substance from a gaseous to the liquid or solid state |
| Density | Mass per volume of a given substance; = M/V |
| Disinfection | Process to kill bacteria and disease |
| DO | Dissolved oxygen |
| Electron | Negatively charged particle present in all atoms |
| Elements | Fundamental chemical substances from which all other substances are made |
| Evaporation | Conversion of a substance form the liquid to the gas state |
| Filtrate | liquid collected after filtration |
| Filtration | Separation of solid particles from liquid by passing mixture through a material that retains the solid particles. |
| Formula unit | Group of atoms or ions represented by chemical formula of a compound; simplest unit of an ionic compound |
| Groundwater | Water which flows underground, such as well water |
| Hard water | Water which contains calcium, magnesium or iron ions |
| Heavy metals | Metals of high atomic mass, generally from the fifth or sixth row of the periodic table |
| Heterogeneous mixture | A mixture which is not uniform |
| Homogeneous mixture | A mixture which is uniform, such as a solution |
| Hydrologic cycle | a.k.a. the Water Cycle, circulation of water between the earth’s atmosphere and Earth’s crust |
| Ion | An atom or group of atoms that has become electrically charged by gaining or losing electrons |
| Ion exchange resin | Material used to remove ions in water treatment |
| Ionic bond | Attraction between oppositely charged ions in an ionic compound |
| Ionic compound | Substance composed of ions |
| Molecular structure | Arrangement and bonding of atoms in a molecule |
| Molecule | Smallest particle of a substance retaining the properties of the substance; a particle composed of two or more atoms joined by chemical bonds |
| Neutral | Neither acid or base; pH 7 |
| Neutralization | Reaction of an acid with a base, in which the characteristic properties of both are destroyed |
| Neutron | Neutral particle present in nuclei of most atoms |
| Organic compounds | Compound composed mainly of carbon and hydrogen atoms; a hydrocarbon |
| pH | Number representing acidity of an aqueous solution; with pH 7 neutral, pH<7 is acidic, pH>7 is basic |
| Photosynthesis | Process by which green plants make sugars from carbon dioxide and water in the presence of sunlight |
| Physical properties | Distinctive characteristics such as state, density, boiling and freezing points, surface tension |
| Polar | Having regions of positive and negative charge, as in polar molecule like water |
| Polyatomic ions | Ion containing two or more atoms, such as PO43- |
| Ppm | Parts per million |
| Precipitate | Insoluble solid substance that has separated from a solution |
| Precipitation | Rain or snow |
| Product | Substance formed in a chemical reaction |
| Proton | Positively charged particle present in nuclei of all atoms |
| Reactant | Starting substance(s) in a chemical reaction |
| Regenerated | Renewed with another chemical |
| Risk factor | |
| Runoff | Water which runs across the Earth’s surface before collecting in surface or groundwater |
| Saturated solution | Solution in which the solvent has dissolved as much solute as it can hold at a given temperature |
| Sewage treatment plant | Factory built for after-use cleaning of municipal water |
| SI unit | Modern term for metric system |
| Sludge | Material which settles out after wastewater treatment |
| Sludge gas | Methane gas |
| Solubility | Quantity of a substance that will dissolve in a given quantity of solvent to form a saturated solution |
| Solute | The dissolved substance in a solution |
| Solution | Homogeneous liquid mixture |
| Solution concentration | Quantity of solute dissolved in a specific quantity of solvent or solution |
| Solvent | The dissolving agent |
| States of matter | 3 forms of matter; solid, liquid and gas |
| Subscript | Character printed below a line of type; in PO43- for example, the 4 indicates the number of oxygen atoms |
| Supersaturated solution | Solution containing a higher concentration of solute than a saturated solution at a given temperature |
| Superscript | Character printed above a line of type; in PO43- for example, the 3- indicates the charge of the phosphate ion |
| Surface water | Water which flow on top of the ground |
| Suspension | Mixtures containing large easily seen particles, which settle out or form layers |
| Turbidity | Cloudiness |
| Tyndall effect | Pattern caused by reflection of light from suspended particles in a colloid |
| Universal solvent | Water |
| Unsaturated solution | Solution containing a lower concentration of solute than a saturated solution at the given temperature |
| Water softening | Removal from water of ions that cause its hardness |
| Water treatment | Either the pre- or post- use processing of water. |