You really need to get some information about the standard deviations associated with those numbers. If the wide excursions are rare you could work with the averages as they represent very manageable waer but if they are not rare then you really only have, IMO, 2 options:
1. Measure each time you brew. If alkalinity and hardness are unusually high then you can probably assume sulfate and chloride are too though that might not be the case. Even if wide excursion is rare you may wish to check alkalinity each time and just not brew on days when it is high.
2. Install an RO system to get essentially the same water whatever the municipality is supplying at the time.
I'd lean towards 2 because it relieves you of having to worry about water.