It is better to flush with distilled water or RO water because it doesn't contain any minerals. If by low EC you mean tapwater? Tapwater contains minerals like cal, mag, etc that will absorb into the plants. With that being said, if you need to flush with tapwater it will get the job done. The main reason to flush is to remove all the harsh chemicals and tapwater will do that. Distilled will give a little smoother, cleaner smoke though. Good luck!