It is mandatory to have a comprehensive water test done on a well before occupancy and a certified lab is recommended. Then it is the responsibility of the (new) owner to have the water treated to correct whatever problems the tests reveal. Whoever the owner contracts with to treat the water is responsible for doing a competent job.

Living on a well is different and more complicated than living on a water system because the homeowner will want to make the water nice and safe. There will be maintenance that has to be done and the water should be routine tested for nitrates and bacteria to make sure whatever treatment you installed is working properly. This is SERIOUS stuff and the health of your family is at risk and it should be done right.

Get a water test from an independent lab. An independent lab has no agenda and won't be trying to sell you water treatment equipment. This is a MUST DO because without it everything is a guess. A quickie water test from Sears or a water softener company won't be as accurate (and possibly not as competent) as from a certified independent lab.

Hit the Yellow Pages and call at least three local water treatment pros. Make sure you call at least one of the big dogs like Kinetico or Culligan for comparison and at least a couple independent pros. DON'T TELL THEM YOU HAD YOUR WATER TESTED.

Give each an opportunity to offer suggestions and provide you with a quote to meet your water treatment needs. IGNORE ANY THAT DON'T TEST YOUR WATER THEMSELVES as they can't speak intelligently to water treatment without knowing what needs to be treated.

Ask lots of questions. Warranty, parts & labor or just parts, how long and on exactly what? Install, permits required, licensed plumber? Routine maintenance and costs? Do they stock parts? Response time for emergency (water leak) calls? If they don't explain things to your satisfaction that is a good indicator of how you'll be treated after the sale.

After they've gone use your water test to compare with theirs. Are all your treatment needs being addressed?

Ask your neighbors if they have any water treatment experience. They might tell you who's good or who to avoid.

Come back here and post the specific recommendations and hardware components with the costs and we'll give you our opinions.

"My first question is: with new construction or new well, is there usually any kind of guarantee from not having bacteria?"

No. The owner is responsible.

Well drillers usually just charge by the foot drilled.

Flow rate it not there problem either.

That is why the contracts often have a stated depth, with an option for additional depth to achieve the desired/required flow rate (or to create storage volume in the bore of the well).

Purity ad depth are not the well drillers problem.