Drinking "alkaline water" to alter a body's pH is more hype than substance.
Here's why.
Gastric fluid in the stomach is highly acidic.
Hydrochloric acid (HCl) is critically important for proper digestion (especially protein) and for correct metabolic function further downstream.
The stomach is supposed to be acidic.
It is unsafe to consume highly alkaline water. Another term for 'alkaline' is 'caustic'.
Drinking water that is mildly alkaline — mild enough to safely drink — is so mild that when it hits the volume of stomach acid it is quickly rendered neutral.
Drinking enough water (volume and/or strength) to alter stomach pH is going to negatively affect digestion and possibly damage the lining.
Different parts of the body — all the way down to individual cells — have a wide range of pH values.
Per the previous paragraphs, any effort at affecting the pH "downstream" is thwarted when the water is consumed.
Besides, it would be guesswork and randomness trying to influence just the right parts and cells by drinking.
"Ionized" water is a misleading term that is used in a carefree manner.
The bonds holding hydrogen (H) and oxygen (O) into water (H2O) are quite strong and it takes a considerable charge to break water back into H2 and O2 molecules.
However, other solids dissolved into water (minerals, for instance) often carry a charge (+ or - depending on a bunch of physics). Those charged atoms or molecules are called "ions".
When ions are present in water people have a habit of saying "the water is ionized".
Technically the H2O is not ionized, it's the particles carried by the water that are ionized.
Similarly, "de-ionized" water is simply water without any charged particles in it.
So the point here is that you can't have 100% pure water (no other particles) and then use electricity to "ionize" it. It just doesn't work that way.
It's only by adding particles of something that you can affect the pH of water.
By the way, de-ionized water is unhealthy.
You might have learned that salt (NaCl) tends towards equilibrium between two bodies of water — in other words, if you have salty water and pure water separated by a thin membrane, water will cross the membrane in order to dilute the saltier side. If the pores of the membrane are large enough, salt will migrate towards the less salty side. Eventually the system reaches equilibrium. This is the principal of forward osmosis.
Reverse osmosis is when you force water through a membrane with pores small enough for H2O molecules to pass along with other very small molecules, but all the larger molecules are too big to pass and simply get flushed away with waste water.
The point here is that de-ionized water messes with equilibrium (aka 'balance') in the body and can cause good minerals to be diluted ('depleted').
Now that you know it's the particles in water that affect its pH (acidic or alkaline) you get to ask the question, "How does a so-called 'water alkalizer' presume to work?"
Is it by adding particles? Well what are the particles and do you need them in your diet?
Is it by trying to charge particles in the water? How is that going to last?
Is it by whirling the water over a magnet? Fancy, but what does that actually achieve?
And in the end, even if the water really does become more alkaline, you get to go back to the comments at top which basically lead to... "why bother?"