The efforts by water suppliers and the Government to get British households switched over to water-metering offer a domestic take on a major global theme.
Demand for water is set to grow exponentially. The term "peak water" – borrowed from the oil industry to suggest we're nearing the limits of a finite resource – is being increasingly used in the numerous water studies by academics, government advisers and investors.
Source: United Nations Environment Programme (UNEP)
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– which water investments to buy
– how different water-oriented investments work
Across western Europe and North America one in three people live in water the UN calls a "water stress" region.
And that's the wealthy part of the world, where both population and urbanisation are increasing but comparatively slowly.
In developing regions, the much more rapid population growth and the emergence of "mega cities" with populations of 20 million are predicted to result in unprecedented water shortages. The populations of Delhi and Mumbai together, for example, at 42 million in 2011, are predicted to reach 60 million in 2025.
This is where specialist investment institutions, which hope to identify the truly long-term themes that will drive returns over the next 20-40 years, build their most powerful case.
They see water as central to meeting the surging need for food and energy in populous countries such as India, China and Brazil, where economic growth is fastest.
They argue that agriculture, today's biggest consumer of water, will gobble up even more as the demand for meat and other water-intensive agri-industries grows. Much of agriculture's existing water use is already unsustainable, they say, effectively reducing the supply just as the need soars.
New forms of energy such as biofuels and shale gas extraction intensify the pressure on water supplies. Add to this scenario the backdrop of rising global temperatures and extreme weather events, which will see flooding alternate with periods of drought, and it's easy to understand the increasing references to "water wars" and frightening predictions of mass migration or nations aggressively annexing water-rich territories and fighting over shared river courses.
Some might think it distasteful to link investment returns with something as essential as water. Others argue that the technologies needed to desalinate, recycle, purify and deliver clean water to growing populations won't ever be developed without huge financial backing.
Either way, it's a major focus of professional and increasingly private investors. Recent performance is helping. Over the past five years water stocks (as measured by the S&P Global Water Index) returned 97pc. The wider stock market, as measured by the FTSE All Share, was up 51pc. The gold price was up 43pc.
Over 10 years, and even 15, water stocks also beat gold, analysts say, although indices tracking the sector don't stretch consistently far enough back to offer conclusive proof.
Because investors can gain exposure to the water theme only via buying shares in utilities, infrastructure and other firms, there are always the risks associated with those individual businesses. And as many innovative water-related industries are linked to sectors such as renewable energy, their shares can be hit even where the core attractions of the water-related proposition are not implicated.
If you're drawn to the idea of water investment here are several ways to play the theme.
Pure water plays
iShares Global Water (index tracker)
This fund tracks the 50 constituent holdings in the S&P Global Water index. Shares in the fund are traded on the London exchange and can be bought via any broker.
PowerShares Global Water (index tracker)
This also tracks an index – but here it's the Nasdaq Global Water index, which comprises 35 stocks. Shares in the fund can be bought via a broker.
Pictet Water (actively managed portfolio)
Pictet is a Swiss-based asset manager specialising in "thematic" investment. This fund, which is structured like a unit trust and can be invested in via major fund brokers, oversees £2bn of global water-related holdings. It has returned 76pc over five years, or an annualised 12pc.
Other funds with significant water exposure
Impax Environmental Markets is an investment trust with a 12-year track record. Currently 20pc of the portfolio is invested in water-related businesses, with the rest backing businesses operating in alternative energy technologies, recycling and waste. The shares are up by 50pc over three years. As a trust its share price sometimes lags the value of underlying holdings, producing a "discount". With the shares trading today at 151p, and underlying assets worth 171p, this discount is now around 12pc.
Hargreaves Lansdown, the broker, has run a screen over other popular funds to identify those with significant water exposure (i.e. between 5pc and 15pc of the portfolio). The results include top-performing and popular funds such as Trojan Income, Royal London UK Equity Income, Invesco Perpetual Income & Growth, First State Global Emerging Markets Sustainability, First State Latin America and Legal & General Global Environmental Enterprise.
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