Tap water or bottled water? What is generally considered better for the perfect cup of filtered coffee. Tap water or bottled water?

The water in London, UK is fairly soft but has loads of calcium in it. 

Bottled water I have heard has lots of salt in it. 

Which is best?
Just think that your drink, coffee, is around 97-98% water so you need quality water to make a quality cup of coffee due the following:



Tap water, beside the calcium, will have additional components and too much calcium will give a taste of acidity to the coffee, calcium makes the water harder.
In order to get a fruity taste from your cup of coffee you need to focus on the balance between magnesium and calcium, magnesium will extract flavor from the beans ... now you know why all the coffee shop coffee taste close to each others and is due the source of water is used( all use tap water) makes them high acidity and requires sugar+cream in order to enjoy that cup :( 
Sodium does make the coffee taste acidic like the calcium does so you need balanced or spring water to see difference or even distilled water but the coffee will loose drastically from the flavor ... unbalanced. 

At least the bottled water you know has added magnesium for taste and is in a balance with other minerals including calcium(not looking does stay in plastic bottles ... that is a different story and think tap water pipes and source of water/process used to make “safe” for drinking)



  Note: I roast the batches of coffee home and in order to feel the
  right flavor tried distilled water, tap water and spring water;
  Currently I use only spring water fresh from the ground and filtered
  so coffee or tea doesn’t require butter, creamer or any other flavors
  added in order to feel the real taste. Same does come to sodium.Even tea does follow same path
  when does come to the water .


One more thing, boil the water and check the sediment left to compare the “tap vs bottled”, “tap vs spring”, “spring vs purified/bottled”.