You could have a solid metal casing pill QV, filled with highly pressurized oxygen and H2. An insulated lead through a small hole, with a wire passed through.The metal casing serves as one electrode, the wire as the other, connected to a car battery and starter coil, or even just car battery and a one-pole switch. The electrode running through the center connected to one terminal, the casing to the other, acting as a sparkgap.
This would explode, creating water. So technically, one COULD have a dehydrated water pill. It'd be explosive,and not hugely stable, but that design would work It wouldn't have any water in it, but a ratio of 1O2/2H2 would form the stoichiometric quantity of H2O upon initiation of the detonation via the inbuilt sparkgap.
There, dehydrated water pill.
Ever filled a balloon with a mixture of hydrogen and oxygen? with enough of a proportion of H2 to allow it to float upwards in air like a balloon full of helium or pure hydrogen (pure H2 can also be used, but a mixture of pure O2 and pure H2 will give a better result)
Tie on a string, soaked in a slowish-burning fuel, a very very long string to allow it to float up into the air a good way, with the end lit on fire, allowing the flame to climb upwards towards the balloon, and it'll go off with a quite surprisingly loud bang, as the detonation velocity of a H2/O2 mixture is pretty high, and the speed of sound propagating through hydrogen gas is remarkably rapid (to safely, totally safely demonstrate just how fast sound propagates in ignited hydrogen, make a solution of caustic soda, and add some tightly scrunched balls of aluminium foil, or a chunk of aluminium metal. Al, being amphoteric, reacts with both acid and base, to release hydrogen (although in the case of acids, it has to be depassivated, aluminium metal is actually very reactive, but it doesn't corrode in air, because on exposure to oxygen, it oxidizes so rapidly, that if one scratches a block of aluminium with a sharp implement, breaking through the Al2O3 layer, it reforms so fast that it reforms the Al2O3 layer as fast as it is disrupted.
And depassivation is required for reaction with most acids, once it has been deprived of the layer of oxide on the surface (which is incredibly thin, nanometers to a few micrometers at most) even dilute (say, 25%) acetic acid or dilute hydrochloric will react rapidly, with hydrogen evolution.
Base on the other hand, needs no such treatment of the Al. caustic soda solution with a piece of aluminium in it will rapidly attack the metal and form sodium aluminate and hydrogen gas. This can be captured to fill balloons to light, either with a long fuse, or lit with a flaming bit of paper on a stick, giving a loud bang.
To see for yourself the great speed of sound propagating through hydrogen, use the caustic/aluminium reaction to make some H2, hold a test tube upside down over the reaction until it is full of hydrogen gas (H2 is the lightest element of all, and is far, FAR less dense than air, so the test tube must be held upside down or the hydrogen would simply float away and out of our planet's atmosphere)
Once full, hold a lit wooden splint to the end of the upside down test tube and listen. It's a classic test for hydrogen, perfectly safe, it's only a small amount in an open-ended inverted test tube. It'll explode, with enough force to put out the flame on the wooden splint, with a characteristic, high-pitched squeaky whooshing pop.
Offensive fact-I REALLY needed a slash, and didn't want to wait to get to the bog, so I turned the tap on to wash it away and pissed in the bathroom sink.
