When you water your potted plants, does the water flow over the edges or run straight to the bottom and out the hole?  Use this to slowly drip water into your pot.

A 2 litre bottle will take about an hour and a half to empty using a 1.0mm hole giving the soil time to absorb the water.

I've included the Fusion 360 .3mf file so you can taylor it to your pots.

Water bottle caps are made of soft plastic so they seal well.  With this, being made of hard plastic, means you'll need either an O-ring washer (~19mm ID) or some grease to prevent leakage around the thread.  Obviously, you'll also need a water bottle with the bottom cut off.

Use variable layer height at a high quality setting so the drip hole is accurate and the bottle threads aren't ‘bridges’.  Use 3 perimeters and 4 bottom layers.

The STL included (360x22x1mm) is for a pot 360mm in diameter with a 22mm thick rim and has a 1mm hole.  If you don't use Fusion 360 and would like another size uploaded, just message me.

If you would prefer not to use a plastic water bottle and, instead, print one with its own reservoir, try: www.printables.com/model/936020-pot-rim-watering-reservoir-parametric