Do you have a softener etc.?
Are you in a drought area? Any new wells in the area?
Watch the pressure gauge on the pressure tank or pump over 10 minutes for a decrease in pressure when no water is used in the building. Did the pressure hold or fall? If it fell, shut off the main water shut off valve and repeat the pressure loss watch of the gauge. If the pressure fell and now didn't, you have a leak on the house side of the valve. If it still fell, you have a leak on the well side of the valve.
You could have a well that just began 'producing methane. To test for it, use like a 2 liter soda bottle filled half full with your water, cap it tight and shake hard for a minute or more. Light a match/lighter and hold it close to the cap as you remove it and squeeze the bottle forcing air out of it through the flame. If the 'air' ignites, you have methane. That assumes you don't have any H2S gas odor in the water.