Securing your belongings at the beach

I saw a tip on Pinterest to hollow out a sunblock bottle and put your keys, cash and credit cards in it. I might consider doing that if I were alone.

Check this out:
http://tinyurl.com/nzflbgm

http://www.amazon.com/WITZ-Surfsafe-Waterproof-Sports-Black/dp/B0065CMDHU/ref=sr_1_3?ie=UTF8&qid=1432933213&sr=8-3&keywords=waterproof+id+case

or this.
I'm not sure I'd put my phone in this and trust that it's waterproof, but for money, passport, etc., there are a lot of options like this available.

One of the disadvantages of travelling alone is that you have no one to watch your back. You can do lots of things but you can 't safely leave your stuff on the beach and go for a swim. Fact of life.

I would take only what you absolutely need and not your phone and either have a swim pouch or have swim gear with a zipped pocket for your key and some money. Money spends fine wet. I have done this snorkeling and I have also put valuables in a zip lock bag and just stuffed it under my suit (works well with a woman's one piece not so well with a guy's suit or a bikini) Sometimes the bag leaks and sometimes it doesn't; I wouldn't trust a phone to it. But it worked fine for my car key, room key and needed money and plastic driver's license. I stuffed the bag in my suit and wore a rashguard long sleeve swim shirt so the bulge wasnt an issue.

Hi Bill, good advice above, especially @janettravels44. In anycase, whatever you decide to do, DON'T leave stuff unattended at the beach. Sadly there's going on a sort of constant cat and mouse game between pickpockets/opportunistic thieves and the Police. Unfortunately there's too much beach to guard and some drifters are known to finance their travelling across Europe with petty crime like this.

Try the human solution.......
Look for fellow tourist ( yes, we do tend to stick out) and approach them to engage in conversation to obtain a small form of comfort in being able to ask if they are comfortable with keeping an eye on your stuff while you take a swim. Yes, this involves risking your stuff with "new friends", but we have found a common bond among tourist is the need to assist with security. The offer of keeping an eye our for each others stuff can be enhanced by offering your drivers license for them to hold in a pocket while they swim; often helps overcome any "reluctant" barriers.
We have used this tactic on a number of occasions in various nations with success while sharing local travel tips and making new friends.

First choice is to leave valuables in the hotel room. To the extent that's an option, it's the safest choice.

Second choice is to never leave anything alone (also true of going to any American beach). Leave someone watching your stuff all the time.

I realize option one and two won't cover all possibilities, especially when traveling alone. Third option is to put your valuables into a zip-lock bag, then put those into a second zip-lock bag to ensure it's waterproof. Ideally, carry no more than a day's supply of cash. Once your stuff is waterproof, you still need to be secure because Barcelona is somewhat famous for pickpockets, so think of a way to keep it inside your shorts/suit. If you pay attention to who is around you, a cargo pocket may be okay for while you're in the water. I wouldn't trust an exterior pocket, however, for hanging around on or near the beach all day.

I understand thefts along beaches to be quite common. I bring a bare minimum of cash to the beach and definitely not credit cards or passport (an exception to standard practice on other days). I learned the hard way not to keep clothes or anything in a day bag that looks like it could have good stuff inside. You'll usually see everyone's towel, shorts, and shoes spread out around their chair or umbrella, easily identifiable as not worth stealing.

Don't leave ANYTHING unattended on a beach, especially in Barcelona!!! Get a waterproof waist belt like previously mentioned, and carry your valuables into the water with you. Leave cameras, phones, keys at home. Be safe! summer is peak pick pocket season in Barcelona. People will steal your shoes!