First: I'm not an expert and don't want to suggest that I am.
I have my doubts, however, that this method of "negatively charging" water actually does anything.
Electricity has this annoying habit of being balanced. As electrons move from place to place, they displace existing electrons, which then displace existing electrons, which then displace existing electrons, round and round, and it completes a circuit -- comes full circle.
And they do this at speeds approaching the speed of light.
So putting a battery in water to get electricity to flow through it cannot impart a negative charge. The electrons flow in from one side and out the other very quickly.
Worse, the electrical repulsive force between two itty bitty electrons is enormous relative to their size. So "negatively charging" your water would send water flying in all directions as the negative charges scrambled to distance themselves from each other, if it were possible to do at all.
The calcium from calcium hydroxide in water is already ionized. It's a 2+ ion. In other words, it has lost two electrons. It is balanced, however by the fact that there are two hydroxide ions (OH-) that have acquired these electrons, and as long as the two are freely intermixing with lots of other calcium ions and hydroxide ions, the net electric charge is still zero, so everyone's happy.
Calcium is a 2+ ion for a very specific reason. The best working model we have of atoms is that they have something called "shells", regions where electrons reside. The first shell can hold only two electrons. The second shell can hold eight (and has two subshells, one that holds two electrons, and the other that holds six). Each shell gets bigger and bigger, but they also get more complicated in terms of where the electrons go in the atom, as these larger shells have even larger subshells within them, each which can hold a certain number of electrons. (The count in the subshells is two, six, ten, fourteen, eighteen... Each shell gains another subshell, so the first shell has only the first subshell, the second shell has the first two subshells [2+6=8], the third shell has the first three subshells [2+6+10=18], etc.)
In general, however, when dealing with ions and reactivity, we're working with either that first shell (two electrons), the second shell (eight electrons), or some combination of subshells in the higher shells, but often times just the first two subshells (so eight electrons).
Neutral hydrogen has one electron (to balance its one proton). Often times, hydrogen will give up its electron to something else to become a free proton -- an H+ ion. Hydrogen can also become an H- ion, by acquiring an extra electron. In that case, it has two electrons in its shell, and that shell (which only has room for the two electrons) is now "full".
But there are two kinds of bonds. One is the electrical kind (positive to negative) -- called ionic, since ions are involed -- and the other is the sharing kind -- called covalent. This is where the atoms share electrons in their outer shells. Where ionic bonds can be broken up in solution (dissolved in water or alcohol or gasoline or whatever can dissolve the substance), covalent bonds don't break up that way. As an example, salt and
Sugar will both dissolve in water, but salt dissolves by breaking apart into sodium ions (Na+) and chloride ions (Cl-), whereas
Sugar molecules just separate from each other, they don't actually break apart. [Note: When the charge is 1+ or 1-, the one is left out and assumed. Only higher charges like 2+, 2-, 3+, etc., include the number. So Calcium with 2+ is written Ca2+, where sodium with 1+ is just written Na+.]
Neutral carbon has six protons and therfore six electrons. The first shell is full with two electrons, but the next shell only contains four electrons. Because that shell has eight positions, there are four free positions that that shell would like to fill, and that's why carbon has four "connectors" when linking to other atoms.
Neutral oxygen has eight protons and therefore eight electrons. The first shell is full with two electrons, but the next shell only contains six electrons. Because that shell has eight openings, thare are still two openings lacking electrons that the shell would like to fill. This is why oxygen has two "connectors" when linking to other atoms.
Elements where these shells are full are called noble gases. These are helium, neon, argon, krypton, xenon, and radon. They don't react because they have achieved some level of perfection, as far as atoms go, and they don't need anything to "complete" them.
Most other atoms, however, would really like to complete those shells by acquiring electrons, or drop down to a "complete" state by giving up the electrons they have in their outer shell. They can do this by either combining with other atoms to form covalent bonds, or they can instead become ions and either acquire or give up electrons.
Calcium is a 2+ ion because it has only two electrons in its outer shell, and to reach a stable shell state, it gives up those two electrons (effectively giving up its incomplete outer shell and falling back to possessing only the more perfect inner shells/subshells).
Hydroxide is a 1- ion because it has an oxygen and a hydrogen covalently bonded (the oxygen is sharing the hydrogen's one electron) bringing oxygen's total number of electrons to seven, but oxygen's outer orbital needs an eighth electron to reach atomic nirvana, so it will accept one of calcium's electrons and become a negative ion.
Since calcium actually has two electrons to share, one calcium atom can pair up with two hydroxide ions as it becomes a calcium 2+ ion.
And so calcium hydroxide is written as Ca(OH)2. It water it becomes either Ca2+ and 2 OH-'s or (about one-fourth of the time) CaOH+ and OH-.
This is a model based on observation about the way atoms interact, and it might actually be a perfect physical model or it might not. I can't argue whether it is or it isn't. But the behavior of atoms and ions matches this model.
Calcium does not want to accept more electrons and go negative. That's too far a stretch to make that outer subshell reach a perfect eight configuration, as it would have to take on six extra electrons to do it, plus an extra ten electrons because the way that shells fill up is more complicated than I'm letting on. It's far easier to drop two electrons than it is to add sixteen, and it would take technology far beyond anything I know to get sixteen extra electrons to join an atom to make a 16- ion for any (human-)observable length of time.
Calcium also does not want to lose more electrons and go more positive. Once it has lost two electrons, the lower subshells, which are filled with their pefect numbers of electrons, resist losing any. It would take some significant effort to strip away another electron.
Now, that doesn't mean that you couldn't be driving the calcium ions back to neutrality, but I have my doubts, because calcium is extremely reactive with oxygen (you aren't doing this in an air-tight container, are you?) and forms calcium oxide. Calcium oxide in water forms calcium hydroxide (lime water -- right back where you started). If this were actually occurring to any appreciable degree, you would then also be producing detectable heat.
Perhaps someone with more experience in this area will chime in.