I have worked with quite hard tap water on several of my previous grows and the plants responded well to it, only in the very end I have seen the detrimental effects - lockout of iron and other micro-nutrients due to high pH. Cannabis is generally pH tolerant but because the pH of my tap water was 8.4 and the alkalinity was high too the soil's buffers struggled in the end. If you are concerned that your water source is also strikingly hard then amend the soil or the irrigation water accordingly, or just get a brita-filter, reverse osmosis etc and mix the tap water with the filtered water to get an overall lower ppm.
good luck