However, almost anything dissolved in the water, in any amount, will affect the pH. Freshly distilled water rapidly absorbs carbon dioxide from the air and reaches a pH of 5.5 in a very short time. Other materials dissolved in the water may have an even more marked effect. Depending on its chemical characteristics, it can either raise or lower pH value. Thus the pH of any solution depends on the amounts and types of materials dissolved in the water. Generally most soil contained in carpet and upholstery is found on the acid side of the pH scale.
Most water based spills are also on the acid side.
The general rule is to use acid on alkaline stains, and alkaline cleaning solutions on acid soils and stains. Naturally, there are exceptions this rule. Some spots and spills can be successfully removed by reconstituting the the spill. This is often why acid spotters are used on coffee. The coffee is in an acid state when spilled, and by adding an acid base spotter, we reconstitute the coffee for removal from the fabric.