Over a century of fertilizing with NPK much of the magnesium in the soil has been depleted as they don't replete magnesium back into the soil,
http://www.canadianlongevity.net/misc/mineral_depletion.php and Magnesium Water (magnesium bicarbonate) recipe below:
Special NOTE: You should know some brands of Milk Of Magnesia like Phillips and Equate contain, inactive ingrediant, Sodium Hypochlorite this is common house hold bleach.
There are some generic brands which contain only Magnesium Hydroxide and purified water, These are CVS Milk of Magnesia original flavor, and Walgreens brand Milk of Magnesia original flavor, and Vitacost Good Sense Milk of Magnesia Original flavor. Check both labels, Active ingrediants and Inactive ingrediants for unwanted chemicals. For best results your milk of magnesia should only contain Magnesium Hydroxide and puridied water. There may be other generic brands which may only contain Magnesium Hydroxide and puridied water as well.
The finished product containes concentrated Magnesium bicarbonate and should be diluted.
To make 4 liters of magnesium bicarbonate drinking water with approximately 125 mg of magnesium and approximately 625 mg of bicarbonate per liter and a pH of approximately 8+ measure and transfer 1/3 liter of the concentrate (333 ml) into a 4-liter container. Fill the container with 3 2/3 liters of purified water (no sodium fluoride), as desired.
To prepare the water follow these steps:
1. Chill a 1-liter bottle of unflavored seltzer, which is fully carbonated water. The seltzer should only contain water and carbon dioxide (CO2). Club soda is carbonated water with a small amount of added sodium and is also suitable.
2. Shake the bottle of Milk of Magnesia well, then measure out 3 tablespoons (45 ml) and have it ready. The plastic measuring cup that comes with the MoM is accurate and ideal for the purpose.
3. Remove the bottle of unflavored seltzer from the refrigerator without agitating it. Open it slowly and carefully to minimize the loss of CO2. As soon as the initial fizzing settles down, slowly add the pre-measured MoM. Promptly replace the cap on the water bottle and shake it vigorously for 30 seconds or so, making the liquid cloudy.
After ½ hour or so the liquid will have cleared, and any un-dissolved magnesium hydroxide will have settled to the bottom of the bottle. Again shake the bottle vigorously for 30 seconds or so, making the liquid cloudy again. When the liquid again clears all of the magnesium hydroxide in the MoM should have reacted with all of the CO2 to become dissolved (ionized) magnesium and bicarbonate.
If a small amount of un-dissolved magnesium hydroxide still remains in the bottom of the bottle as a sediment it may be ignored.
This 1 liter of concentrated magnesium bicarbonate water will have approximately 1500 mg of magnesium and approximately 7500 mg of bicarbonate. It should be kept in the refrigerator. You may note that the sides of the bottle “cave in” when the liquid clears. This is a sign that the reaction is complete.