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You may think it's because you brewed it differently, but my guess would be that the differences between the water where you first tasted it and where you live are to blame. Water greatly affects coffee, and it's different everywhere you go. What's tricky here is figuring out which is better: Is one water superior to the other, or are they just different? I would argue that there is no one perfect water, but rather many perfect waters. It really depends on what you want to get out of your coffee. After way too many years on the fringe, the topic of water quality is finally getting the attention it deserves in our industry. Considering that water makes up the majority of the beverage we've chosen to prepare, this makes sense. What is it that we want and need our water to be like in order to make tasty coffee, all the while protecting the equipment that we are using? There is already quite bit of information out there on how to protect your equipment from scaling, but not nearly as much on what type of water chemistry makes the best coffee. The reason is that it's subjective. Different types of water will change the way the coffee tastes, and depending on what flavor profile you're looking for, that will make a difference in what type of water filtration you should be using. What's Making Your Coffee Taste Bad? Before you can decide what type of water treatment you need, you have to know what to test your existing water supply for. So let's talk about some of the main factors that will affect your coffee's flavor in a negative way. Iron is terrible for coffee, for instance. Preparing coffee with water that contains concentrations as low as 10 milligrams per liter will affect not only the flavor but also the color of the coffee. Even with a low concentration, iron combines with phenols in the coffee to produce greenish colors. Iron can be detected at levels as low as 1 milligram per liter and can be difficult to filter; in many situations a reverse osmosis system will be needed. Additionally, the pH in water is an important factor and can be difficult to manage. A pH of 7 is neutral; below 7 is acidic, and above 7 is alkaline. You will always want to be as close to 7 as possible. A water supply with a high pH and the presence of calcium is more likely to scale than a supply with a low pH and the same amount of calcium. While pH is a key factor for water quality, it's also one of the most difficult to control. It's near impossible to manipulate pH without adding total dissolved solids (TDS), and removing other components will change the balance of the water. The Carbonate System refers to many factors within water including acids and bases, total alkalinity, pH, and certain metals—especially calcium and magnesium—all of which are interrelated when it comes to water quality. Total alkalinity measures the water's ability to neutralize acids. Hardness relates to the presence of calcium and magnesium in the water. Water with a high concentration of these metals can lead to scale deposits. In very hard water, you will have chlorides, sulfates, carbonates, and bicarbonates that are dissolved in solution. Chlorine and chloramines are oxidizing substances that destroy harmful pathogens occurring in all municipal water supplies. They affect coffee flavor by prematurely oxidizing aromatics and oils, so they must be removed. Handy Tools for Assessing Your Water These are some of the most common problems a barista will find in his water supply, and will need to address. Sadly, I don't have space to cover them all in an article, so I recommend you familiarize yourself with the Langelier Index if you haven't already. The Langelier Saturation Index (LSI) is an equation used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. The LSI is expressed as the difference between the actual system pH and the saturation pH. In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral-dissolving or scale-forming properties. The index takes into account all measurable aspects of the carbonate system. This index can be used to predict the physical effect that the existing quality of water will have on equipment. The math to compute this can be rather difficult, so you can use an index calculator. Here is the URL for the one the Specialty Coffee Association of America (SCAA) recommends: www.csgnetwork.com/langeliersicalc.html. Addressing water quality and determining the solutions are daunting tasks. What you will need to do first is decide the level of water quality necessary for your business. Figuring out a TDS range where your coffee tastes best is a great place to start. I know many people in the coffee industry who love the way their coffee tastes with water with a low TDS, and many others who prefer it in a higher range. In general I think a good range would be between 125 and 175 parts per million. Carbonates and bicarbonates slow the flow of water throughout the coffee bed, especially when the concentration exceeds 100 milligrams per liter. Sodium and potassium at low concentrations can actually add to the perception of sweetness in coffee. At higher concentrations, sodium will increase sourness. Potassium emphasizes the bitterness in the phenolic compounds in the brew.