I did some measurements and this is output:
| EC | Ph |
Water from the pipe (tap water) | 562 | 7.2 |
On day old tap water | 562 | 7.5 |
Distilled water | 2 | 6.8 |
Boiled water (1 day old) | 508 | 8.1 |
So realy hard to get under 500 EC without reverse osmosis or using disilled water.