Water is said to be acidic when the pH is below 7;
water is said to be basic when the pH is above 7.
A pH value of 7 is considered neutral, which means it's neither acidic nor basic.
pH values in waterbodies range from less than 4 to over 12.

It's important to note that each one of the 14 increments on the pH scale represents a ten-fold change in acidity. For example, lake water with a pH of 5.0 is ten times more acidic than lake water with a pH of 6.0; water with a pH of 4.0 is 1,000 times more acidic than water of pH 7.0 (Scales used in this manner are "logarithmic" like the Richter scale used to express earthquake intensity.)

The Role of pH in Waterbodies
pH influences aquatic biological systems in a variety of ways. In the early years of the 20th century, pH was regarded as the "master variable" and was routinely studied by aquatic scientists in an attempt to understand its complex role. Waterbodies in the low end of the pH scale (more acidic) are of particular interest to scientists concerned about the effects of acid rain on aquatic plants, fish, and wildlife.

In Florida
Waterbodies in the Florida LAKEWATCH database have pH values ranging from less than 4 to nearly 12. Approximately half of the Florida lakes sampled have pH values between 5.8 and 7.8.

The location of a waterbody has a strong influence on its pH. For example, lakes in the Okefenokee Plains lake region in north Florida (in Baker, Columbia, and Hamilton Counties) tend to have pH values below 4.8, and lakes in the Lakeland/Bone Valley Upland lake region in central Florida (in Polk and Hillsborough Counties) tend to have values above 7.5.

Fish, plants and wildlife have different sensitivities to pH. For example, the young of some fish species cannot survive in water that has a pH below 5.0. However, with few exceptions, lakes with relatively low pH in Florida are able to support healthy fish populations.

Most living organisims in Florida systems appear to be well-adapted to acidic conditions, possibly because low pH seems to be a naturally-occurring environmental factor. Consequently, many aquatic scientists do not consider acid rain to be as great a threat to Florida's waterbodies as it is to those in other parts of the United States.

Health Concerns
pH in lakes and rivers is not known to cause significant human health problems. However, when pH is lower than 5.0, some people experience eye irritation.

pH is important in municipal drinking water supplies. The acceptable range for pH for drinking water is generally from 6.5 to 8.5. This range, however, is not based on direct health concerns, but is primarily based on minimizing the corrosion and encrustation of metal water pipes. However, pH can affect drinking water supplies, as described below.

• When pH is lower than 6.5 or exceeds 8.5, chlorine in drinking water supplies becomes a less effective disinfectant.
• When pH is lower than 6.5 or exceeds 8.5, chlorine in drinking water supplies can contribute to the formation of cancer-causing trihalomethanes.
• When pH of drinking water is in the acidic range, it can cause copper pipes and lead soldering in pipes to dissolve.