Cambridge Water for Great Coffee

Cambridge is an outlier in terms of water chemistry in the Boston area. Most cities and towns around Boston source potable water from the Massachusetts Water Reservoir Authority system; Cambridge goes it alone and uses its own systems (except on an emergency basis – shortages – when it pays for MWRA supplementation.) There are historical, practical and cost reasons behind this approach, and Cambridge provides safe water at lower cost than if it were to source from the MWRA. However, Cambridge water goes through intensive treatment and as a result, has three characteristics which create challenges for coffee shops.

Cambridge tap water is high in total dissolved solids (TDS). Pre-filtration, the TDS at our shop is over 450ppm and the official Cambridge data puts it at 472ppm (as of 2018). To put this in context, MWRA water ranges between 50-150ppm and the Massachusetts Department of Environmental Protection puts the threshold for public drinking water at 500ppm. Water with a high concentration of existing dissolved solids is generally less effective as a coffee flavor solvent – which means that untreated, coffee brewed in Cambridge will tend to be under-extracted. What solids are dissolved also influences the flavor of the water (and thus the coffee) as well as the balance of what is pulled out of the ground coffee. Assuming a proper balance of minerals and bicarbonate, we believe that between 75-150ppm water is optimal for extraction and flavor.

Cambridge tap water is high in total dissolved solids (TDS). Pre-filtration, the TDS at our shop is over 450ppm and the official Cambridge data puts it at 472ppm (as of 2018). To put this in context, MWRA water ranges between 50-150ppm and the Massachusetts Department of Environmental Protection puts the threshold for public drinking water at 500ppm. Water with a high concentration of existing dissolved solids is generally less effective as a coffee flavor solvent – which means that untreated, coffee brewed in Cambridge will tend to be under-extracted. What solids are dissolved also influences the flavor of the water (and thus the coffee) as well as the balance of what is pulled out of the ground coffee. Assuming a proper balance of minerals and bicarbonate, we believe that between 75-150ppm water is optimal for extraction and flavor.

http://talk2bio.com/wp-content/uploads/2017/02/ph-scale-1.jpg

As a result of water facility treatment, Cambridge water also has a surprisingly high PH, 9.1 according to Cambridge Water Department figures. One of the final steps in the water treatment process in Cambridge is to increase the PH for corrosion control to reduce the propensity of water to leach lead and copper from the service lines and home plumbing systems. Although the water is treated with sodium hydroxide, not sodium bicarbonate, it has a distinctive salty, chalky, baking soda like taste to it.

Finally, Cambridge water has a high chloride count – officially 236ppm (vs 50ppm or so in most MWRA locations, and a maximum DEP guideline level of 250ppm.) Under heat and pressure, the chlorides can acidify (think hydrochloric acid and sulfuric acid) to the extent that water that started with a base PH, ends up being surprisingly acidic. Indeed, Cambridge is known in the espresso machine manufacturing industry for having a disproportionate number of boiler failures related to acidic water and some manufacturers now require Cambridge cafes to install sophisticated filtration systems as a warranty condition.

http://hmdigital.com/what-is-tds/

At Broadsheet, we have made significant investments in water filtration . We have a large primary filtration system of the sort used in many breweries. All water that is not fed to the toilets goes through this carbon and sediment filter combo. This helps, but can’t come close to solving the TDS, PH and chloride problem. Water intended for consumption is thus fed into a secondary system: an efficient reverse osmosis unit which produces water that is pretty close to distilled. Extremely low TDS water, however, doesn’t make for tasty coffee (it can be harsh, over-extracted, and thin). The tank of our RO system is equipped with a sensitive TDS meter, connected via a control loop to a peristaltic pump that drips a mineral solution into the tank to allow us to achieve and precisely maintain our target TDS count and mineral balance. We keep this steady throughout the year (TDS levels in the water supply fluctuate seasonally) which allows us to minimize the variables with which we must contend in brewing and to optimally and consistently extract our coffee. The primary filtration system and RO unit aren’t cheap, but we feel they more than pay for themselves by protecting our equipment, and of course by allowing us to consistently brew the best coffee and tea we can – which is after all our raison d’etre.

For further reading on the topic of water and coffee, Chris Hendon and Maxwell Colonna-Dashwood’s Water for Coffee is the go-to book on the subject, and Scott Rao, Matt Perger and Jim Schulman (and others I’m sure I’m omitting) have all also experimented with and written extensively on the subject.


Additional information on water in Cambridge and the MWRA is available via the following links.

Cambridge’s water treatment methodology:

https://www.cambridgema.gov/~/link.aspx?_id=A61A0E4F43C646B3A508ECAF9EE14E71&_z=z

Cambridge’s most recent (2017) water quality report:

https://www.cambridgema.gov/~/media/Files/waterdepartment/labfiles/CCR/2017ccrcambridgerevised.pdf?la=en

MWRA’s 7/2018 water quality report:

http://www.mwra.com/monthly/wqupdate/pdf/cy2018/082018.pdf

MA Department of Environmental Protection Drinking Water Guidelines:

https://www.mass.gov/files/documents/2016/10/us/310cmr22_372_16185.pdf

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