Depends on the ph of your water. Many will preach that the microorganisms within the soil will act as a buffer, keeping the ph stable. This is true.... to a point. If your water is coming out the tap around 7-7.5, I wouldn't really trip to hard, I've seen it done with little to no adverse affects. But if its coming out above 8, bring that shit down homie! Id rather make a dent in the microorganisms in the soil then have full blown nutrient lockout, that's just me though. If your really worried about it, Im positive they have natural alternatives.