According to the , the SplashDrone 3+ can carry up to 1kg. This is without any accessories, no camera. This is more than enough to carry a parachute and its deployment and triggering system.
To safely land a drone like the Swell Pro SplashDrone, I would recommend a system like the Opale Safetech ST60X made for the Inspire and drones up to 4.9 kg. This system is light 220 grams and the SplashDrone should have no problem carrying it.
Then you need to find a way to power the system, with a small extra battery for example. That will add a few more grams, 50 at most, that's negligible.
For triggering, you can choose a system like the Mayday which will automatically trigger the parachute when it detects a failure. This is very light at 14 grams.
Thankfully the SplashDrone 3+ has an emergency motors cut off procedure as shown in the picture below :
As seen in SplashDrone user manual, page 37 :
Having an extra external battery, a dedicated control system and the ability to cut motors mid flight is great because the whole parachute system is now independent and autonomous. You will be able to easily unmount it when you don't need it and you won't jeopardize the waterproofing of the SplashDrone.