Here are the candidates tested:
Rear, left to right: Arrowhead "spring water" (actually bore water), Kirkland "drinking water" (reverse osmosis artesian well water, with some minerals added back), San Pellegrino (spring water, carbonated so do not use in espresso though good cold with a bit of chocolate syrup added), Brita-filtered tap water, Bunnahabhain (not tested - this was for after the after-test party). Front, left to right: Brita "professional" test kit, water from my espresso machine(softened) hot water tap, Honolulu tap water.
Results (hardest to softest):
| Water | Hardness (German[?] Degrees) | Hardness (ppm) |
| S. Pellegrino | 6-7 degrees KH | 107-125 |
| Arrowhead | 6-7 degrees KH | 107-125 |
| Tap Water | 2 degrees KH | 36 |
| Kirkland | 0-1 degrees KH | 0-18 |
| Brita filtered tap | 0-1 degrees KH | 0-18 |
| Espresso machine | 0-1 degrees KH | 0-18 |
(Imprecision is intrinsic to test kit. Note use of 1KH->17.86ppm conversion for hardness units.)