Socially responsible investing is a worthy concept that's based on avoiding so-called "sin" stocks. These are companies that manufacture guns, tobacco, alcohol, pollute the environment or put people in dire financial straits, such as gambling stocks.

In contrast, so-called "virtue" companies manufacture products that aid the environment or heal people and help them fight addictions, as well as those that comply with strict ethical business practices. I should mention that there is also a weird factor in socially responsible investing that streamlines investors toward mutual funds and investment clubs, which have heavy religious and conservative undertones. However, let's leave that factor aside for now.

It is also a fact that socially responsible investing is often very limited. There is plenty of historic evidence pointing toward the selection of companies that comply with the social criteria as often having a poor future outlook. So, how can you equate the two? Where can you find companies that will both keep your conscience clear and make you money at the same time?

One option is the water industry, which is perhaps the world's next big moneymaker. A while back, I talked about Canada and its potentially huge role in supplying the world with fresh water. However, I'm sure many socially responsible investors would argue that we shouldn't profit from something that everybody needs to have free access to, such as water.

I believe there is a flaw in this argument. Water is a global right -- There are no ifs, and, or buts about it. However, the state of the world's water infrastructure is fragile. So, while experts, activists, and governments are all demanding and mandating new water projects, their execution will largely depend on the private sector to see them through. And if the private sector is expected to shell out money in order to build a new infrastructure, then we cannot impose profit restrictions on it at the same time. This is why investing in the water industry could be both socially responsible and profitable.

So, what should investors be looking for? Well, I'm not just talking about selling water as a commodity, although that is the first thing that springs to mind. The industry is also comprised of utilities, which use the power of water to generate energy. It also includes companies that lay pipes and manufacture valves, build water-treatment facilities, or design products and technologies for water purification or desalination.

When it comes to the size of this sector, let me tell you, it is enormous. More than 700 different companies provide products and technologies for water infrastructure, while the entire sector is estimated at $1.7 trillion worldwide. Surely the playing field is huge enough for you to pick something interesting and potentially profitable for your portfolio, particularly if you are a socially responsible investor.