"I just took two different water test on our "new" 102 year old house" box store DIY tests or a comprehensive water test by a certified, independent lab?

Although you post that "Everything came back in an ideal range" how about posting the test results in detail? Then we can speak intelligently about treating your water.

Hardness, iron, manganese, copper, chlorine, arsenic, PH (we know), TDS, bacteria, nitrates (we know) for starters.

We'll also need to know the # of people and bathrooms in the home and whether there are any high water use appliances like an uber-shower or Jacuzzi.

A PH of 5 is VERY aggressive water and that will need to be treated for sure and the sooner the better for your plumbing, fixtures, and appliances. I can tell you that no simple add-on house filter will address the PH problem. Treating a low PH problem will usually add hardness to the water so along with whatever hardness is in the water now, you'll most likely require an ion exchange softener.

PH 5
Alkalinity 0
Chlorine 0.2
Hardness 50
Iron 0
Copper 0
Nitrate 2-5
Nitrite 0
Lead undetectable

We were very surprised by the PH. The prior owners lived in the house for 45 years without treating the water. The dishwasher is about 10 years old and the washer is probably more than 15+ yrs and they both work.

3 people live in the house, with two full baths, two half baths,washer, and dishwasher. We will probably be adding another full bath in the next 5 years. Additionally, my in-laws stay with us for a few weeks twice a year, so we would want a system that would be able to handle 5-6 people without a problem.

I really appreciate your help. Thanks!

If you'd be so kind as to add the delineators to the numbers... hardness = 50 what? Grains, PPM, pounds, gallons?

No bacteria test?

Well water changes so perhaps that PH of 5 hasn't been that for 102 years? You might also run the PH test again to make sure.

sorry, all measured in parts per million.

My water source is not a well. It is water from the village where the house is located.

Is your water supply EPA or state certified?

If your village water system is state or EPA monitored then they can provide you with a copy of the water tests they are required to routinely do.