How important is water ph?

I've had a quick search around but couldn't pin down any answers on this. I'm sure they're out there though. My water is quite hard and the ph is between 7.4-7.8 How vital is it that I get the ph down before watering? What problems will this cause to growing in soil (All-Mix) if I don't address this? I'm trying to keep things simple. Any help much appreciated.

After reading up a bit more and speaking to a friend. I've been using Ph-down to get my water to around 6.0 for my babies and seeds. I'm going to be using All-Mix for the remainder of the grow. Let me know if I'm not doing the right thing! :thumbsup: