Water (H₂O) is comprised of one oxygen and two hydrogen molecules, and the bonds between and among them lead it to be a unique and fascinating biological molecule. As we know, depending on the coffee beverage (espresso versus drip-based) water can contribute 94-98% of the ‘coffee’ beverage as we consume it (Illy and Viani 2005). Considering this, our coffee beverages are important contributions to human dietary intake for hydration. Water, after all, is necessary to sustain life. Water (H₂O) molecules themselves are known as polar because the hydrogen atoms and oxygen atom have differing electrical charges. The hydrogens have a slight positive charge, while the oxygen has a slight negative charge. Because these individual molecules have a polarity, they can attract other molecules with charged ions. The water molecules bind together with hydrogen bonds, which are very strong and are the reason ‘droplets’ of water form and have the propensity to stick together. Temperature also affects the rate at which compounds are soluble in water, as with increasing temperature all reactions speed due to the altered energy of the molecules.

That being said, not all water is equal! In many countries there are strict public health standards for drinking water supplies to ensure healthy and uncontaminated hydration. In others, citizens would be lucky to secure this precious resource. In the United States, the Environmental Protection Agency works to regulate this at a federal level, and states or cities within them are able to create even higher water standards if they deem them warranted. Of course, these standards do not have to do with creating artisanal specialty beverages, but serve a purpose of health and safety.

It also turns out that water is not just H₂O. In this way again, not all waters are equal, even within the United States or within one city. Dissolved substances, mineral contents, and additives all make their way into ‘safe’ drinking water and ultimately influence our coffee cup. Obvious ‘other’ components in water you may be familiar with include calcium, chlorine, fluoride, iron, sulfates, or micro-organisms like bacteria. All of these can easily influence the taste of the coffee in the cup and have characteristic off-flavors and aromas.

The Standards

Odor: Should be odor free. This is an olfactory measurement. Obvious odors such as those caused by sulfates, bacteria, or other micro-organisms, chlorine, or phenol compounds, for example, should be treated for and removed.

Color: Should be clear. This is measured visually. All issues, such as cloudiness, red or orange tinge, or particulates, should be treated depending on the specific issue.

Chlorine: 0 mg/L. Chlorine is added to water by municipal systems to prevent biological contamination (micro-organisms). The World Health Organization reports that chlorine is present in most disinfected water at concentrations of 0.2–1 mg/liter (WHO 2011). It usually presents with a taste (think pool water) or odor. SCAA’s standard is strict about removing all chlorines from water due to its large potential affect on the cup.

Total Dissolved Solvents (TDS): between 75-250 mg/L TDS, with a target of 150. TDS is a key way we measure water in the coffee industry. There are federal standards for TDS to enable safe drinking water, but again these are not designed for optimal beverage consumption. The EPA recommends less than 500 mg/L TDS for drinking water in its non-mandatory secondary drinking water recommendations. However, this standard does not define what makes up that TDS, which can be any variety of minerals or dissolved solids. A high TDS generally indicates hard water.

Calcium Hardness: 1-5 grains per gallon (gpg) or 17-85 mg/L, with a target of 3-4 gpg or 51-68 mg/L. Calcium hardness is the amount of hardness created specifically by calcium ions in water. Total hardness is a measurement of the cations in water and can be created by minerals with a positive charge. The primary components of hardness are calcium (Ca++) and magnesium (Mg++) ions. Dissolved iron (Fe++) and manganese (Mn++) also satisfy the definition of hardness, but typically make up only a very small fraction of total hardness. Hardness is not bad for health, but considered more of an aesthetic factor. The presence of some dissolved mineral material in drinking water is typically what gives the water its characteristic and pleasant taste. However, too much can be responsible for excessive deposit buildup on coffee brewing equipment, termed ‘scale’, and can lead to functionality problems if left unresolved.

Total Alkalinity: At or near 40 mg/L. This is the measurement of the concentration of negative ions in the water. Alkaline compounds such as bicarbonates (such as baking soda), carbonates, and hydroxides remove hydrogen ions (H+) and lower the acidity of the water. Total alkalinity is measured by measuring the amount of acid (e.g., sulfuric acid) needed to bring the sample to a pH of 4.2. At this pH all the alkaline compounds in the sample are “used up.” The result is reported as milligrams per liter of calcium carbonate (mg/L CaCO₃). Too much alkalinity can affect extraction and coffee flavor.

pH: 6.5-7.5, with a target of 7. Pure water should have a neutral pH of 7. With more hydrogen (H+) ions, the pH of water decreases, which means it has a higher acidity. Water becomes basic when there is a high presence of hydroxide (OH-) ions, which can result in water having a bitter taste. Both of these situations can alter the brewing reactions and the cup. Typically, alkaline water (high pH) used to brew coffee results in a ‘flat’ taste.

Sodium: Less than 30 ml/L, with a target of 10 mg/L. The World Health Organization reports that most water contains less than 20 mg/L but levels in some countries can exceed 250 mg/L (WHO 2011) . Water softeners can also contribute to the sodium content of water. Salts can affect the way sweetness or sourness is perceived in the mouth, and therefore high amounts should be avoided in water used for brewing coffee.