Yup and even people in the same town can have different water qualities. I would save yourself the trouble and forget about using tap all together. Invest in a RO/DI and know its almost never your water thats causing you tank problems.
This is the safe answer. I've had too many spills with the RO, and have found that PERSONALLY I'm ok with just the DI. This doesn't mean that someone one town over (or as mentioned above, the guy next door) will be ok with just DI.
If you want to get a feel for your water, get a TDS meter, some good test kits, and try to borrow or buy a phosphate meter. This will give you a general idea of how your local water is. Knowing that mine is generally ok, I still use the DI to polish it.