The byproduct of ionized water is acidic water. Acidic water has  many uses, but one of them is as a natural disinfectant or antiseptic.

• Acidic water, with a pH of between 2.6 and 4, will kill germs if you let it sit for a minute or two. 
• Acidic water with a pH of 2.5 and under will kill germs (bacteria and viruses) on contact. Note: This fact has been proven in scientific applications to kill bacteria and other germs. 

Low PH Acidic Water (2.5 pH)

It is usually difficult or impossible to get acidic water to be lower than 2.5 pH unless you use sodium in the ionization process somehow. Most water ionizers do not have a sodium injection system to get this lowest-acidic-water, but I will show you how to use rock-salt-sodium with your water ionizer, as a simple little trick to get just the right pH (2.5 pH) acidic water to kill germs on contact. I call this kind of water "low pH acidic water".

1. First, before starting this procedure, you should check with the manufacturer (or sales representative) of your water ionizer to ensure sodium won't damage it.
2. Next, collect a few spray bottles for however much acidic water you want to make. 
3. Then get out the rock salt chunks and put them in the water ionizer's mineral port. (Note: I never use granulated salt, because this could harm the water ionizer. Don't use the tiny chunks made for salt grinders either. Only use chunks of about 1/4 inch diameter.)
4. If you're using a water ionizer that doesn't have a mineral port, set up an external mineral port and put the rock salt in there. Further down this article is a section on how to use an external mineral port.
5. Start pouring ionized water at the slowest flow-rate possible and strongest setting for the machine.
6. Collect the alkaline water out of the top spout and use this for drinking or cooking purposes. Note: The strong alkaline water can also be used as a de-greaser or cleaning agent for washing floors, doing laundry, etc. It can also be used as a pre-wash for more difficult viruses (to break down the outer defenses a bit before subjecting it to the strong acidic water)
7. Collect the low acidic water out of the bottom acidic-water-hose. Test it to determine the actual pH-level. Add a little vinegar if you want, to bring down the acidity even more.
8. When you are finished collecting acidic water, empty the mineral port of all rock salt chunks and then pour about another cup or so of regular ionized water to flush the sodium out of the water cell. Note: Whenever you add sodium to your water ionizer use this caution. Always make sure to remove the sodium when done and rinse the machine by pouring about a quart or so of regular ionized or filtered water (no sodium added) before leaving it.

In this video I demonstrate using my water ionizer to use acidic water to fill up my spray bottles with disinfectant acidic water. 

Alternate Method of Making 2.5 pH Disinfectant Acidic Water

Sometimes I don't want to go through the hassle of making acidic water using rock salt in the mineral port (as above). So, in that case what I do is collect acidic water out of the bottom hose while I'm ionizing my regular alkaline ionized drinking water. This acidic water will usually test about 5 or 5.5 pH. Then I will add about 1/4 cup vinegar per quart of acidic water and fill each spray bottle with this solution. The extra added vinegar to the already pretty acidic water will bring down the acidity to 2.5 (per my many tests).  As long as you know the pH is 2.5 or below you can be sure it will kill germs on contact. But, the only way to test pH that low is to use a properly calibrated pH meter.  PH reagent test drops will only show a range of pH from 4 to 10. If you don't know for sure what the pH of the water is, I suggest you use a precautionary measure of letting the acidic water sit on the surface after spraying for a couple of minutes before drying it (or you could just let it evaporate on its own). 

Different Uses for Medium-pH Acidic Water

Do not confuse using the lowest acidic water [for killing germs] with beauty water or water for watering the plants. One would use only a mildly-low acidic water [around 4 – 6 pH] for those uses.

Your Source Water Influences the pH You Will Be Able to Get

My St. Louis source water is pretty good (medium-hard), and using the Athena water ionizer without adding rock salt will normally give me low enough acidic water (lower than 4) even without this trick, but not all customers will get the same results. That's why you need to test your acidic water and not just assume you got these results. 

How to Store Acidic Water

Acidic water stores best in either plastic or glass. Do not use it in or near metal. One very nice thing about acidic water is that it will maintain the low pH indefinitely. I have tested it six months after pouring and found it to be the same low acidic pH as when first poured. Another good thing is that it will not go bad. No germs or anything whatsoever will grow in it, so it stays fresh and usable forever (or until it gets used up or evaporates).

Benefits of the Lowest Acidic Water

I like to fill up my spray bottles with the lowest acidic water I can get, for germ-killing purposes. As you can see in the video, above, using this little trick allows me to get an extremely low pH, plenty low enough to kill germs on contact. I love cleaning my toilets and counter-tops with this all-natural, chemical-free, disinfectant/anticeptic acidic water. 

As an anticeptic, it can be just sprayed right onto a cut or you can use it as a soak. 

I also will use the lowest acidic water to descale tile in the bathroom. It makes the tile sparkle with cleanliness. 

Another use is that I soak my water testing probes in the lowest acidic water sometimes [if I want to de-scale the probe safely]. 

So, this is a very handy trick to know, and I thought I’d pass it on to you. The only caution is that I suggest to do this only rarely, such as once a month, i.e., not on a daily basis, because you could over-work your water ionizer.

By the way, the acid water, which comes out of the bottom hose while I'm pouring my ionized water for drinking, is perfectly good for skin, hair, beauty water, watering plants and general cleaning. There is usually no reason to go for the lower acidic water. But it’s nice to know you can get it if/when you want to.