Do you ever wonder if the pool is clean as you dip your toe in to test the temperature? I think that is a common concern for swimmers who use public pools. In a properly maintained pool, several variables are managed to ensure that the water is safe for you. The one we always think of is chlorine, but without also managing filtration, pH, and total alkalinity levels, you probably don't want to go into the water.
Chlorine is very effective in killing organisms in the water, but it turns into a gas and readily leaves the water. That explains the strong chlorine smell you sense when walking into a pool room. Chlorine can also irritate the eyes, skin, and mucus membranes. Because chlorine leaves the water in the form of a gas, the chlorine level needs to be closely monitored. Bromine is a much better antiseptic. Bromine does not gas off and therefore you will not notice a chlorine like odor from a bromine pool. Bromine levels do not change as quickly as chlorine levels. Bromine does not irritate the mucus membranes, skin, or eyes. So, why not use bromine in all pools? Bromine is significantly more expensive than chlorine. If you tend to be sensitive to chlorine, try to find a pool that uses bromine as an antiseptic.
Whenever you add either chlorine or bromine to water, the pH changes, so a second chemical needs to be added to adjust the pH. You can have good antiseptic levels and no organisms in the water, but have a pH level that will irritate your skin and eyes. So, it is not as simple as adding chlorine to keep the water clean and safe. The pH level is something that needs even more attention than antiseptic levels. The pH can rapidly and suddenly change, so yet a third chemical is used to prevent this, a buffer.
Now, all of the above can be well managed, but without filtration, the pool water will look cloudy and dirty. Nobody feels comfortable entering a murky pool. So, pools have big filters to remove all the tiny particles that form in the water. These filters need to be regularly changed. A poorly maintained pool will have a bacterial or algae bloom or turn cloudy from a clogged filter within 48 hours.
So, the next time you get into that clean, clear, warm water, remember that it is that way due to the frequent daily maintenance that goes on behind the scenes.