We've had well water and septic for 17 years
We simply do not drink the water, we are considering a reverse osmosis water filter, but until then, we'll continue to drink bottled water.
Now - for the well: we had to have the motor replaced -a couple of years ago. The cost on this was ~$2500. The upside - we've not had a water bill in 17 years. The cost for any well repair is very dependant on how deep the well is. Pumps go out with no notice. So - it is something that just needs to be dealt when it happens.
Our septic system needs to be pumped about every 3 years (this is a state -regulated thing.) This costs about $200 every 3 years.
Now - the downside on the septic. We do not have, nor will we ever consider having a garbage disposal. NOPE - a septic would cost about $20,000 to replace. The cost to replace a septic is also a downside.
In our state - when a home is sold, there needs to be some testing on the well and the septic system. If there is anything "amiss" with either, the seller will not be able to sell the property unless it is fixed.
Hope this helps!