# How does alkalinity affect pool water?

Swimming pools are generally kept at a $p H$ of around $7.5$. Acidity of public swimming pools would be fairly tightly controlled.
If you travel round the world, you will notice that tap water varies from place to place. In some places (Europe), tap water is generally hard (i.e. $p H$ $\ge$ $7.3$); this makes it hard to build a lather from soap. In other places, and I think specifically of the Pacific Northwest, Washington, and British Columbia, water is soft, $p H$ $\le$ $7.0$; soap is very easy to lather and the water tastes good. So-called water-hardness describes water that is slightly alkaline. Of course, the $p H$ scale is logarithmic, and even slight changes in $p H$ represents large changes in acid (${H}_{3} {O}^{+}$) concentration.