What is the buffering capacity of water?

Pure or distilled water has relatively no buffering capacity. The buffering capacity of water can vary somewhat if the water comes from an impure source such as a river or pond.

Buffering capacity refers to how well a solution can maintain a narrow pH range when an acidic or alkaline solution is added. Some buffering capacity test kits measure KH, also known as carbonate hardness. A higher reading from the test kit, indicates a high KH and a high buffering capacity, meaning the solution provides better resistance to pH changes. A result under 4.5 dH indicates a lower KH and a limited buffering capacity.