I've been wondering this for a long time

Question

how come that when you make a hole in the ground and fill it with water to simulate a lake, the water sips down to the ground. but when in the real thing, it doesnt?

Answer 1

When you dig - you are only going through the topsoil. This is naturally free draining.

Lakes and ponds are based on the subsoil - usually a compacted clay or rock - which are impervious, so the water just sits. The natural groundwater also has it's own level - so a hole any deeper will fill up naturally.

Answer 2

Mr.P is somewhat right. It depends on the ground and how it perks. When a septic system is being installed they will do a perk test to check drainage. If the ground is clay{or something like} it won't drain very good, if it is sand{or something like} it will drain to fast. Location and soil is what determines weather you'll have a pond lake or just a big hole in the ground