pH is the unit of measure used for the amount of acidity in a liquid. The lower the pH level that a liquid has, the more acidic it is. Pure water has a pH of about 7, depending on its temperature. Liquids that rank with a pH value of 7 are considered neutral, in that they're neither acidic nor basic.
When water becomes more acidic, it's quite corrosive. This becomes dangerous as the water passes through plumbing, as it breaks down the pipes and leaches metals like lead, copper, iron, and zinc into a home's water supply. These metals are toxic and can harm us if they get into our drinking water.
Most refrigerator water filters can remove these metals if they find their way into your drinking water. But it is possible you'll need to look into other water filtration solutions, like whole house filters or reverse osmosis filters.
The best way to check your home's water for dangerous pH levels are with a WaterSafe All-In-One Home Drinking Water Test Kit.