I see two main issues: a) the photos are are too dark- thats why the water and sky colors look murky b) their hue is shifted too much towards red - this is why they are not turquoise enough

both of these things can be easily corrected with any image processing software. For example this is what i came up with using gimp to give a basic idea of what I would change (this is by no means perfect, just a general idea):

My recommendation for better sea photography:

Good exposure in camera. It is quite common to under or overexpose images of the sea when using automatic exposure because it has a combination of dark blues (deep sea) and reflections, and this fools the automatic exposure system. To get the most out of your photos in camera I recommend using manual exposure (see for example the "sunny 16" rule) a good place to start during early afternoon is usually 1/400 sec, f8, iso 200 and then adjust based on the histogram.

Circular polarizer If you want to get even more brilliant colors of the sea I highly recommend a circular polarizing filter, it gives a look that you cannot achieve by post-processing alone. This is what was most probably used to create the image you referenced as the perfect water color. It gives a distinctive look that not everyone likes, but brings up the saturation, decreases the sky brightness (makes clouds really pop) and enhances the colors of the sea (darks become darker and lights like dunes become lighter). You can look through photos (ex. on flicker) to see if it is a look you like before you decide to buy one.

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Things to consider to improve image quality of similar photos, response to the "camera specs" provided in the question

• A UV filter doesn't do much in digital photography, except guard the lens surface from scratching. Sometimes it can increase flair when shooting very high contrast or against a light, and very slightly reduces image quality (I personally don't notice the difference in practice if it is kept clean). FYI I would defiantly not use it in combination with a polarizing filter if you decide to get one.

• A lens hood, on the other hand, may help increase micro-contrast in some situations especially in the full sun if you are not using one already.

• I notice you are using the Canon kit lens, if you stop it down to by 1-2 stops (to around f8) it may give you more crisp photos (more "micro contrast") and less of a vignette (you can see it in the photos you posted, it becomes more noticeable when you increase brightness and contrast), it may not make a huge difference, but if you're looking to get the most out of the gear you own, this maybe something to try.

• If you decide to use a polarizing filter there are basically 3 things to know: 1) rotating it changes the strength of polarization 2) polarizing strength will depend on where the sun is with respect to the scene (at 90 degree angle from the sun it will be the strongest) 3) wide angle shots look weird because of no. 2, to avoid this try not to use a focal length much below about 25mm on an APSC sensor camera (around 35mm on a full frame).