I agree, looks like a Waveraider. You can look at the HIN number stamped on the ski to find out what year it is (last 2 digits of that number). There will be a model number on the ski someplace (look in back or in the engine compartment)my best guess is around 94 or 95 Wave Raider 700?
700cc 2 cylinder 2 stroke engine. Pretty relaible model, but remember you are looking at around a 15 year old ski. Top speed around 50-53 mph (my guess).
You said the magic words: "Water Test". That will tell you more about the ski than anything else possibly could. If it starts easily cold, throttles up quickly in the water, transitions well from high to low throttle and low to high, handles the turns without bogging, and doesn't smoke excessively then the engine and pump system are probably OK.
After that, I'd look at the hull and hoses for cracks, check the interior for signs of corrosion, ask about salt water use, ask if/when the top end and carb has been cleaned and rebuilt, take a flashlight and look at the impeller and wear ring, how many hours on it? I think if you do a water test and it passes, you can skip checking the compression (some others may disagree).
The 700 cc motor was fairly common and used on several skis, so parts are still fairly easy to find.