Dr. Monika Fekete explores what occurs in the water treatment process and how new additions and omissions can impact water flavour and coffee profiles.
One spring morning I went for a leisurely 20-kilometre walk around the Maroondah Reservoir, a pristine lake near the Yarra Valley, north-east of Melbourne.
The clear water looked inviting for a swim, but a number of stern warning signs quickly discouraged such ideas. The reservoir holds water from protected catchments in the area to provide the city with one of the cleanest sources of drinking water in the world – no wonder that authorities do their best to guard this precious supply.
Even though we are lucky to have a high-quality water supply, water still needs treatment to be considered safe for drinking. However, each step affects the taste of water for coffee.
Treatment plants usually are located near reservoirs and are operated by the local water supply company. This is where all the necessary treatment happens – we’ll get to this in the steps below. Distribution of drinking water after treatment is then passed on to multiple retail companies.
What the floc?
When it comes to treating water, we first need to filter out impurities, such as clay particles, plant debris, and even microscopic living creatures. The problem is a lot of this stuff is too small to simply catch on a filter membrane, and their mostly negative charges tend to stop them sticking together. To get around this, engineers add positively charged chemicals (typically aluminium salts) to the water. Once neutralised, the particles stick together into so-called flocs, which are easily filtered out. The aluminium sulphate stays in the water, but is said to have a sweetish taste – so no major consequences.
What’s the deal with chlorine?
The next step is disinfection, most commonly using chlorine. In water, chlorine makes a weak acid called hypochlorous acid, which kills bacteria. Importantly, a small level of chlorine needs to stay in the water after it leaves the treatment plant to keep it protected from water-borne diseases. Although this residual chlorine is completely safe to drink, it can strongly affect taste.
But why do some waters taste more chlorine-y than others? How much chlorine you need depends on the quality of the water source, transportation systems, and on how long it takes for the water to reach individual households. The maximum allowed level is five parts per million (ppm), which is still completely safe to drink. In Melbourne, a low level of only 0.03 – 0.3 ppm concentration does the job, which is below the level most people can taste. However, in Perth, for example, 0.5 – 1.5m ppm is necessary – just a little lower than the levels in swimming pools. In more bad news for Perth, chlorine taste is stronger in warmer water.
What else is added to drinking water?
Fluoride (at around 1 ppm concentration) is added to drinking water to prevent tooth decay. Despite some persistent myths around potential adverse health effects, more than 60 years of accumulated evidence shows that it is not only safe, but works very efficiently. According to a paper published in July 2017, Water fluoridation: dental and other human health outcomes by the National Health and Medical Research Council, fluoride reduces tooth decay in adults by 27 per cent. Flouridation doesn’t change the taste of water.
The chlorine and fluoride additives do slightly lower the pH of the water (making it a bit acidic). To balance it out, the engineers add a small amount of an alkaline salt such as lime (calcium oxide and hydroxide), caustic soda (sodium hydroxide), or sodium carbonate. The amount added is too small to really affect
natural water hardness.
One result of water treatment is that many features of the water that reaches our taps are standardised across different locations. Sediments and organics are settled out, heavy metal levels are strictly controlled, and microscopic life is eliminated by chlorination.
Water hardness, on the other hand, is not regulated from a health perspective. This way, it remains a distinctive signature of the water’s original source. As we discussed last issue (see BeanScene October 2017 edition), hardness comes from contact with minerals rich in calcium, magnesium, and carbonates that the water passes through.
Depending on the natural environment in the catchment area, water hardness can vary greatly. Looking at the water hardness map of Australia (see image on left), we can see that Victoria and Tasmania have the softest water, while Western Australia and South Australia have some of the hardest. Data varies even within the same city, let alone whole states. Looking at capital cities only, on average, general hardness in Hobart is barely above 10 ppm, while it reaches nearly 100 ppm in Brisbane and Adelaide. Canberra, Sydney, and Darwin sit somewhere in between. High TDS in many regions of Western Australia, South Australia, and Queensland increase our perception of a salty taste in these waters. However, Queenslanders have little to complain about this year, as Toowoomba was judged to have the best tasting water in Australia, ahead of last year’s champion sample from Barrington, Tasmania. In a similar fashion to coffee tasters, tap water competition judges use a flavour wheel.
Does the best drinking water make the best coffee? Not necessarily. We know from experience, both from brewing coffee with tap water at different locations and from optimising brew water with mineral concentrates (described in the previous issue) that calcium, magnesium, and bicarbonate all have a big impact on taste.
Some level of water hardness is generally needed for the best coffee outcomes. If there’s not enough minerals in the water, coffee can end up tasting flat and hollow. Too much, however, can be detrimental not just to taste, but to the espresso machine as well. It’s a fine line. Hard water is responsible for limescale build-up in brewing equipment, so you may need to use further purification steps (also known as softening) to reduce hardness in the water.
Now that we know what goes on behind the scenes when treating water, I’ll be thinking twice before jumping into reservoir lakes. Each drop in our water supply is precious, and each drop undertakes a remarkable journey even before it ends up in our taps to drink.
Dr. Monika Fekete is the Founder of Australian Coffee Science Lab.
This article features in the December 2017 edition of BeanScene Magazine. Subscribe here today to see the FULL copy: www.beanscenemag.com.au/subscribe