like maybe many others I don't have a Water Strider mount. But it has been brought to my attention that it can be rather easily obtained with Timewarped Badges. These can be used to buy Angler reputation tokens (each will give 300 rep) from the MOP Timewalking Vendor on the Timeless Isle. Here is a little breakdown:
When you start with 0 reputation like me with the anglers, you first need to get to Revered. This will be 3000+6000+12000 reputation, 18000 in total. 18.000/300 = 60 Tokens. 50 Timewarped Badges each makes 3000 badges.
As soon as you hit Revered, fly to Nat Pagle (Angler Quartermaster) and get the Grand Commendation of the Anglers for about 40g. This will double the rep gained for The Anglers by 100%. So we can calculate with 600 rep per token.
21.000/600 = 35 Tokens for 35×50=1750 badges. So, for 4750 badges and another about 4k gold you'll get your Water Strider mount. And a little tip: The tokens are bound to your account, so you can buy tokens with alts and send the tokens to your designated strider buy toon. And while I was writing this text, I bought the mount with 0 rep half an hour ago.
Happy Water Striding!
EDIT: Thanks to Barrens-Chat: "before you fly to Nat Pagle for the Grand Commendation badge (to double your rep gains), buy the 35 tokens needed to get from revered to exalted. Even though the badge will say 300 rep, once you use the Grand Commendation badge the tokens will give you 600 rep. That way once you hit exalted you will already be at Nat to buy the mount."
EDIT 2: I got so heated in my happiness that my math is off. The first step requires 21.000 for 3+6+12 is 21, not 18. So to complete the math here: 21.000/300 = 70 Tokens before flying to Nat Pagle. That totals it to 5250 badges. Thanks to OhwowTaux for pointing that out.