Brewing Coffee with instant hot water tap In my office they have a tap with (boiling) hot and cold filtered water system - its designed for hot drinks, and is fine for black tea.  I assume it dispenses at around 100 degrees, though I have not measured it.  The cold tap gives chilled water - I'd assume 5-10 degrees.

I brew my coffee using an aeropress, with about 2 spoons worth of coffee and the standard paper filter. Filled up to a mark between the 2 and 3 marking on the aeropress.

What comes out has a slight metallic, bitter taste.  I do not get this at home where I use a standard kettle (either leave it to boil and cool for a few minutes, or use my new kettle that can specify the temp - I generally use 85-90 degrees)

I have tried to eliminate the problem thus:


Different beans (2 different bags of fresh preground ground coffee, with both "standard for cafetiere grind" and espresso grinds).  Grinding at work is not an option and doing at home is too annoying.
Different storage (I thought the metal tin I was storing in was imparting bad flavour) - I have now got a glass kilner jar which is air tight and stored in a dark drawer
Washing the paper filter before use (I dont do this at home normally)
Using the inverted method (with the same, or slightly less grounds)
Using another breakout area (with the same system) in case the normal one is broken/dirty/etc


None of this makes a difference so I assume it is down likely down to the temperature of the water being too hot.  

What is the best (quickest and least fussy) way of improving my brew?

I have considered (but not yet attempted):


Adding a small amount of cold water before adding the hot (approx 1/4 cold to 3/4 hot) then brewing as usual.
Add the hot then add a splash of cold.
Mixing in another cup and adding that - this is undesirable as I already have to carry the coffee jar, aeropress and cup to the kitchen and back.


What is the best means to get a better brew?
Is it, by any chance, demineralised/distilled water, with no minerals added back in?

Aside from temperature (which you should check - it's OK if it's cooler, but too cool is no good, and knowing the temperature will help you modify other parameters), it's important to have high quality, odour-free water that is free from impurities and that has the correct mineral content. The SCAA actually specifies water standards (see here). In many developed parts of the world, tap water is fine. However, demineralised water is NOT fine. It will underextract.

One solution*: Buy bottled mineral water (like Evian or a cheaper alternative), which usually has too HIGH a mineral content, and blend it with the filtered water from the dispenser. This may seem hard core, but it'd be good as an experiment to see if it cures your woes.


Joke only intended after the fact