Bottled water – a hugely successful money-spinner and no better than tap water. Still, my wife thinks it’s good for her so I guess it probably is.
But I’ve found a good use for empty plastic bottles. Drill a small hole (about 6mm) in the plastic cap, fill the bottle with water (tap water or rainwater, not bottled water!). Put the cap back on and push it cap-end first into compost.
A perfect low-tech, no cost solution for slow-watering indoor pot plants (if you don’t mind looking at plastic pots) and greenhouse plants, particularly if you’re going away for a week or two in summer.
I haven’t yet worked out why some of the bottles empty a lot quicker than others. It might be because the water puddles under the cap when the compost is wet enough, which would be a brilliant invention as it would prevent overwatering. Or it might be because air can’t get into some of the bottles causing a partial vacuum, in which case drilling a tiny hole (2 – 3mm) into the end of the bottle would solve it. That’d be the Mark 2 version.
Vicci Stocqueler: I do this, and also freeze it so it drips more slowly and absorbs into my hanging baskets.