This depends on the dissolved materials.
Decrease
Titanium dioxide is not dissolved in water.
Maybe the water has some CO2 dissolved in it.
pollen === Pollen? Hardly! The pH of river water is affected by a variety of factors: dissolved CO2 from the air (making it slightly acidic), organic acids from the soil, and by dissolved minerals such as calcium carbonate.
2-4 ph
Titanium dioxide is not dissolved in water.
Decrease
This depends on the dissolved materials.
Maybe the water has some CO2 dissolved in it.
Ammonia is a basic gas. It shows high ph if it is dissolved in water.
Hair does not have a pH, because it is (and will) not dissolved in water. Water with shampoo having pH = 5.5 reacts neutral when used for hair washing.
Rain is naturally somewhat acidic (pH 5.5) due to carbon dioxide dissolved in the water. Problem acid rain also has dissolved sulphur dioxide and nitrogen oxides which form sulphurous and nitrous acids.
Metal hydroxides dissolved in water form basic solutions, with a pH greater than 7.
Some salts dissolved in water have an acidic pH.
When is dissolved in water this type of salt has a pH over 7.
Yes, because it is a base.