If you are bad at remembering to water your plants, Grant Thompson has a great hack for you: just use nappies! In the above video, Thompson shows how you can use any pack of nappies to make "super-absorbent hydro-soil" for your plants.
Basically, you pour four cups of water into a standard nappy — "new or gently used", says Thompson — and rip it open to dump the hydra crystal inners into a bowl. Add a little more water and mix it up. The crystals will have absorbed all the water.
Combine equal parts of the crystals and regular potting mix. There's your super-absorbent hydro-soil!
One adult-sized nappy (or diaper, as the Americans have it) makes over 12 cups of hydro-soil, Thompson says.
Some folks at Garden Web suggest that instead of a diaper, you can pick up a container of just the hydra crystals instead, making it a much cheaper proposition.
Diapers Help Your Plants Grow [Grant Thompson - "The King of Random"]