Magnesium bicarbonate supplementation
Why use magnesium bicarbonate?
Magnesium bicarbonate liquid is my default magnesium supplement recommendation for a few reasons:
- It's easier to confirm the purity of the magnesium hydroxide used to make magnesium bicarbonate than with the ingredients used in typical magnesium capsules. Most of the companies making magnesium capsules buy their magnesium from third parties, which seems to have led to at least one case of consumers being mislead.
- It's inexpensive when made at home. When made using magnesium hydroxide it runs around 10 cents per 100mg of magnesium, and that's including the carbonated water.
- It's absorbable (see this experiment).
- It's much easier on the digestion than some forms of magnesium. Some people work their way up to very high levels of intake with it, which carries its own risks, but isn't even achievable with some other forms of magnesium.
Making it at home (recommended)
Making your own magnesium bicarbonate only requires adding a source of magnesium hydroxide (a powder you can order online or milk of magnesia from a drugstore) to carbonated water. Here's how I do it:
Recipe for making a using :
Supplies needed:
1 liter bottle of carbonated water. Any bottled water whose sole ingredient is carbonated water (sometimes listed as "water, carbon dioxide") will work. These may be labeled "seltzer water" or "sparkling water." You could also carbonate your own source of water using a home carbonation system, allowing you to use the water and bottle of your choice. 
Pure magnesium hydroxide powder. A 250 gram bag will let you make around 69 liters of concentrated magnesium bicarbonate. I buy this one (manufactured in Japan). 
A 25mL graduated cylinder (optional). This makes the measuring and pouring easier, reducing the risk of messy bubblesplosions. I use this one (a 10mL one seems better at first, but this 25mL one is better sized for quickly pouring in the powder). If that isn't an option, you'll need a 1/8 measuring teaspoon and a way to quickly pour in the powder, such as a funnel with a wide enough mouth to keep the powder from clogging it.
Directions:
- Chill the carbonated water. This helps keep the carbonation in solution. I prefer using a freezer to get the water colder than the usual refrigerator temperature. At a typical freezer temperature of 0°F, this seems to take around 2 hours for a 1 liter bottle. It's fine if the bottle freezes, so long as it doesn't burst.
- Gently remove the bottle from the freezer or fridge. Too much agitation can increase the amount of carbonation that escapes. If the bottle has frozen, allow it to unfreeze before continuing.
- If you have a graduated cylinder, fill it with 4.3mL of the magnesium powder. Otherwise, measure 7 eighths-of-a-teaspoon of into something that will allow you to pour the entire amount into the bottle quickly. It's ok if your measurements are not exact: if you have too much magnesium hydroxide, the excess will settle to the bottom. If you have too little, your magnesium water just won't be as potent.
- Mix the ingredients. Unscrew the cap from the carbonated water, quickly pour in the magnesium powder, and reseal the cap tightly.
- Shake it. Shake it for a good 30 to 60 seconds, ideally while mumbling the lyrics to Stayin' Alive.
- Refrigerate the bottle. I'd suggest leaving it for at least an hour to give the reaction time to occur.
- Shake the bottle again. This will help ensure that the remaining magnesium hydroxide reacts.
- Enjoy your magnesium water!
- Each ounce of this concentrated water will have around 40-44mg of very-absorbable magnesium, so it's good to start with small amounts. It tastes pretty good if you add a splash of it to juice, or you can just add some to plain water.
- I'd suggest keeping it refrigerated with the cap on tight.
- I'd advise against shaking the bottle before use, even if you see white flakes settled on the bottom. They're unlikely to react any further, and may be harder to digest than the straight liquid part.
- Along the same lines, I'd advise against drinking the last bit of water if any white flakes have settled.
- The bottle should be good for a week or two, although more magnesium will settle out with time.
Supplies needed:
2 liter bottle of carbonated water. Any bottled water whose sole ingredient is carbonated water (sometimes listed as "water, carbon dioxide") will work. These may be labeled "seltzer water" or "sparkling water." You could also carbonate your own source of water using a home carbonation system, allowing you to use the water and bottle of your choice. - Pure magnesium hydroxide powder. A 250 gram bag will let you make around 69 liters of concentrated magnesium bicarbonate. I buy this one (manufactured in Japan).
- A 25mL graduated cylinder (optional). This makes the measuring and pouring easier, reducing the risk of messy bubblesplosions. I use this one (a 10mL one seems better at first, but this 25mL one is better sized for quickly pouring in the powder). If that isn't an option, you'll need a 1/8 measuring teaspoon and a way to quickly pour in the powder, such as a funnel with a wide enough mouth to keep the powder from clogging it.
Directions:
- Chill the carbonated water. This helps keep the carbonation in solution. I prefer using a freezer to get the water colder than the usual refrigerator temperature. At a typical freezer temperature of 0°F, this seems to take around 2.5 hours for a 2 liter bottle. It's fine if the bottle freezes, so long as it doesn't burst.
- Gently remove the bottle from the freezer or fridge. Too much agitation can increase the amount of carbonation that escapes. If the bottle has frozen, allow it to unfreeze before continuing.
- If you have a graduated cylinder, fill it with 8.6mL of the magnesium powder. Otherwise, measure 14 eighths-of-a-teaspoon of into something that will allow you to pour the entire amount into the bottle quickly. It's ok if your measurements are not exact: if you have too much magnesium hydroxide, the excess will settle to the bottom. If you have too little, your magnesium water just won't be as potent.
- Mix the ingredients. Unscrew the cap from the carbonated water, quickly pour in the magnesium powder, and reseal the cap tightly.
- Shake it. Shake it for a good 30 to 60 seconds, ideally while mumbling the lyrics to Stayin' Alive.
- Refrigerate the bottle. I'd suggest leaving it for at least an hour to give the reaction time to occur.
- Shake the bottle again. This will help ensure that the remaining magnesium hydroxide reacts.
- Enjoy your magnesium water!
- Each ounce of this concentrated water will have around 40-44mg of very-absorbable magnesium, so it's good to start with small amounts. It tastes pretty good if you add a splash of it to juice, or you can just add some to plain water.
- I'd suggest keeping it refrigerated with the cap on tight.
- I'd advise against shaking the bottle before use, even if you see white flakes settled on the bottom. They're unlikely to react any further, and may be harder to digest than the straight liquid part.
- Along the same lines, I'd advise against drinking the last bit of water if any white flakes have settled.
- The bottle should be good for a week or two, although more magnesium will settle out with time.
Supplies needed:
- 1 liter bottle of carbonated water. Any bottled water whose sole ingredient is carbonated water (sometimes listed as "water, carbon dioxide") will work. These may be labeled "seltzer water" or "sparkling water." You could also carbonate your own source of water using a home carbonation system, allowing you to use the water and bottle of your choice.
Bottle of milk of magnesia. Look for brands where the only ingredients are magnesium hydroxide and purified water. I have some suggested brands here. If your brand comes at some concentration other than 1200mg magnesium hydroxide per 15mL / tablespoon, you'll have to adjust the recipe below. 
A glass measuring cup with a spout for quickly pouring the milk of magnesia (optional).
Directions:
- Chill the carbonated water. This helps keep the carbonation in solution. I prefer using a freezer to get the water colder than the usual refrigerator temperature. At a typical freezer temperature of 0°F, this seems to take around 2 hours for a 1 liter bottle. It's fine if the bottle freezes, so long as it doesn't burst.
- Gently remove the bottle from the freezer or fridge. Too much agitation can increase the amount of carbonation that escapes. If the bottle has frozen, allow it to unfreeze before continuing.
- Shake the bottle of milk of magnesia, and measure out 3 tablespoons / 45mL of milk of magnesia. The included measuring cup is fine for this, but you should transfer the final amount into a measuring glass with a spout so that it's easy to pour quickly. It's ok if your measurements are not exact: if you have too much milk of magnesia, the excess will settle to the bottom. If you have too little, your magnesium water just won't be as potent.
- Mix the ingredients. Unscrew the cap from the carbonated water, quickly pour in the milk of magnesia, and reseal the cap tightly.
- Shake it. Shake it for a good 30 to 60 seconds, ideally while mumbling the lyrics to Stayin' Alive.
- Refrigerate the bottle. I'd suggest leaving it for at least an hour to give the reaction time to occur.
- Shake the bottle again. This will help ensure that the remaining magnesium hydroxide reacts.
- Enjoy your magnesium water!
- Each ounce of this concentrated water will have around 40-44mg of very-absorbable magnesium, so it's good to start with small amounts. It tastes pretty good if you add a splash of it to juice, or you can just add some to plain water.
- I'd suggest keeping it refrigerated with the cap on tight.
- I'd advise against shaking the bottle before use, even if you see white flakes settled on the bottom. They're unlikely to react any further, and may be harder to digest than the straight liquid part.
- Along the same lines, I'd advise against drinking the last bit of water if any white flakes have settled.
- The bottle should be good for a week or two, although more magnesium will settle out with time.
Supplies needed:
- 2 liter bottle of carbonated water. Any bottled water whose sole ingredient is carbonated water (sometimes listed as "water, carbon dioxide") will work. These may be labeled "seltzer water" or "sparkling water." You could also carbonate your own source of water using a home carbonation system, allowing you to use the water and bottle of your choice.
- Bottle of milk of magnesia. Look for brands where the only ingredients are magnesium hydroxide and purified water. I have some suggested brands here. If your brand comes at some concentration other than 1200mg magnesium hydroxide per 15mL / tablespoon, you'll have to adjust the recipe below.
- A glass measuring cup with a spout for quickly pouring the milk of magnesia (optional).
Directions:
- Chill the carbonated water. This helps keep the carbonation in solution. I prefer using a freezer to get the water colder than the usual refrigerator temperature. At a typical freezer temperature of 0°F, this seems to take around 2.5 hours for a 2 liter bottle. It's fine if the bottle freezes, so long as it doesn't burst.
- Gently remove the bottle from the freezer or fridge. Too much agitation can increase the amount of carbonation that escapes. If the bottle has frozen, allow it to unfreeze before continuing.
- Shake the bottle of milk of magnesia, and measure out 6 tablespoons / 90mL of milk of magnesia. The included measuring cup is fine for this, but you should transfer the final amount into a measuring glass with a spout so that it's easy to pour quickly. It's ok if your measurements are not exact: if you have too much milk of magnesia, the excess will settle to the bottom. If you have too little, your magnesium water just won't be as potent.
- Mix the ingredients. Unscrew the cap from the carbonated water, quickly pour in the milk of magnesia, and reseal the cap tightly.
- Shake it. Shake it for a good 30 to 60 seconds, ideally while mumbling the lyrics to Stayin' Alive.
- Refrigerate the bottle. I'd suggest leaving it for at least an hour to give the reaction time to occur.
- Shake the bottle again. This will help ensure that the remaining magnesium hydroxide reacts.
- Enjoy your magnesium water!
- Each ounce of this concentrated water will have around 40-44mg of very-absorbable magnesium, so it's good to start with small amounts. It tastes pretty good if you add a splash of it to juice, or you can just add some to plain water.
- I'd suggest keeping it refrigerated with the cap on tight.
- I'd advise against shaking the bottle before use, even if you see white flakes settled on the bottom. They're unlikely to react any further, and may be harder to digest than the straight liquid part.
- Along the same lines, I'd advise against drinking the last bit of water if any white flakes have settled.
- The bottle should be good for a week or two, although more magnesium will settle out with time.
Buying pre-made bottles
I'm only aware of a few sources of pre-made magnesium bicarbonate liquid:
- United States: MagBicarb claims around 7710mg/L of magnesium, but the elemental amount is probably around 1286mg/L (see yerrag's comment here).
- Australia: Unique Water at 1300 305 795 (or www.uniquewater.com.au, but the site has been down for over a month) has 125mg/L of (elemental) magnesium. The bottles are BPA-free.
- Hong Kong (with plans for worldwide distribution): Longevity Water is a magnesium bicarbonate water, but I haven't been able to find information on the concentration of the magnesium.