A few days ago I posted a modern house with a pool in a pond/lake. I've been asked by a few people to make a tutorial on how I did it, so I made one.

Hope it's helpful!

The house:
http://www.modthesims.info/download.php?t=351955

Step 1.

Choose where you want to build your pool.


Step 2.

Use the 'level terrain' tool to level the terrain where you want to build the pool.
You can also Build the pool first and create a lake/pond around it when done.


Step 3.

You have to delete all objects directly around the pool, except for foundations, walls and fences.


Step 4.

If you want a fence around the pool, place the fence first. You can't place a fence on the pool walls as you could in TS2.


Step 5.

Build the pool.


Step 6.

Use the 'lower terrain' tool to lower the terrain around the pool as much as you want.


Step 7.

Change the pool walls/floors if you want to.


Step 8.

Done!