So for this bad boy you can load up any of your properties. What you want to do is buy yourself a Pond Neptun and get that thicc thing in the ground. Now, stand in it, fill it with your hose, switch to the paint tool, and empty it with the “A” button. Repeat this until that beautiful achievement pops.
This took me two attempts. On the first I did the process 10-15 times. On my second attempt (I reloaded the game) it popped on the third fill up. I don’t know if this was a glitch, or if the game was simply upset that I was there.
Edit: My issue, and the issue others have had, is that you CAN NOT use your office. It must be a different property.