To add to this great comment, there are areas around LA designated as the "Ground Water Recharge Basins". This is basically big, temporary ponds to capture water before it gets to the ocean. This water is then naturally filtered into the ground and get pumped back up later for urban use.

https://www.pointblue.org/science_blog/attractive-and-beneficial-groundwater-recharge-basins-can-be-both-for-people-and-wildlife/#:~:text=These%20are%20natural%20or%20artificially,groundwater%20level%20in%20the%20aquifer.

You can see these at the north end of the 605 fwy, near the Santa Fe dam, as an example. Smaller, local projects aim to utilize the soil areas around public roads to channel and hold water so more can soak into the ground. They look like small riverbeds meandering around other landscapes. 10 fwy on ramps in the San Gabriel area seems to have this feature as well as the median on the upper Santa Anita Blvd.

Efforts are being made but probably more can be done.