The new Water World map coming in v0.77.0 is the first map to be available to every civ in the game, and was designed to be fully playable by every civ. By far the hardest to get started though will be the Reptilians, as Crystalline is a vital Reptilian resource, and it is not present on the Water World map. That said, it is still possible to get a Reptilian colony up and running on Water World, but it will take careful planning and resource management at the beginning in order to get the colony off the ground.
As long as your map starts you with at least one Ore Deposit and one Aluminum Deposit within harvesting reach, you should be able to spin up a successful Reptilian base. If you start the map and do not have access to at least one each of those, you might as well quit and restart. Remember that the Construction Probe is a flying unit, so you can move it to different islands in search of the resources you need. You want to start on an island that has both, or an area that has two islands close enough together that a small bridge will be able to connect them, as you cannot waste your initial resources on excessive bridge building.
The strategy is to basically get to the Medium Range Star Gate as soon as you can while spending as few resources as you can to get there. Once you have the Medium Range Star Gate, you can import Crystalline and then build the synthetic kind using the Enslaved Extremeobug. The Medium Range Star Gate is not cheap though, and will require more Antanium than you start out with, meaning you will also need to build an Antanium Impactor. You will also need two Microreactors in order to power everything.
So to begin, you should build 1 Microreactor, a Powered Materials Silo, and a Slave Gate. Then produce Gold, Ore, and Aluminum bugs and start harvesting. When you can afford it, first build the second Microreactor, and then the Antanium Impactor. After that you are just waiting until you have enough resources to build the Medium Range Star Gate.
Once you have the Medium Range Star Gate, you are basically home free and can build anything you want, as you now have the ability to import and export all Reptilian resources. The trick is getting to that point, as building one extra structure can put you in a resource position where you will never be able to recover, and will ultimately lead your map to a dead end.
To build the Synthetic Crystalline Deposit, you will need to import Crystalline and Rum from the Medium Range Star Gate. You can export Gold or Aluminum to generate the required funds. Once you are growing Synthetic, your map should be good to go. Just make sure you find a nice secluded place for it, as Crystalline Spread can be problematic for a settlement.
Although it's harder to get started, the Reptilians can have a fully functional and self sufficient Water World base. It just takes planning and patience!