Our planet's water supply is an incredibly valuable resource that we need to protect, and worrying new figures show between 30-50 percent of it is being stolen - meaning that water isn't paid for or counted.

This theft occurs when people and companies obtain water illegally - often for agricultural purposes. That could mean getting treated water that should be paid for free of charge, or obtaining water in ways that go against environmental guidelines.

The problem itself isn't new, but most of us have no idea it's happening. This report looks into the under-researched issue, and offers some idea for fixing the systemic problem.

The conclusion? While individuals and companies are doing the actual stealing, the newly published study points the finger at political, legal, and institutional frameworks that aren't properly set up to protect the precious water that we all rely on.

The root causes of water theft aren't being correctly addressed, the researchers say, the value of water is not being appreciated, and illegal actions aren't being properly punished – all of which means that a huge amount of water is lost through theft every single year.

"Ongoing water shortages occur on all continents, increasingly compounded by climate change," write the researchers in their published paper.

"By addressing likely drivers of theft at an individual scale, we may prevent irreversible harm to all water users."

There is some debate about what counts as water theft – or even if it exists at all, as water is a natural resource that we all have access to. But the team looked at three separate case studies involving improper water use: growing marijuana in California, strawberries in Spain, and cotton in Australia.

While these cases varied widely in everything from social norms to local regulations, they did highlight some common themes.

All three activities are water-intensive, and all three case studies show the effects of market demands on water theft – stealing water is simply very profitable, most of the time, and certainly more profitable than following environmental regulations (in the Spanish case study, regulations in place to protect a migratory bird site).

Uncertainty about water supplies, caused both by human actions and natural variations in rainfall, is also one of the key drivers of water theft, the study suggests.

A lack of any real policing is a factor too – if there's no chance of being caught, people will steal water even when they don't need it.

On the other hand, effective monitoring and a widespread assumption of high compliance in a society (where everyone believes that everyone else is being honest) help to reduce water theft, the study authors point out – along with having a plentiful water supply in the first place, of course.

One of the big changes we can make, according to the research, is to make sure that penalties for stealing water are both significant and properly enforced – especially in remote and rural areas.

Publicly exposing theft can also help in some situations. This financial and social rebalancing makes stealing water less cost-effective and less accepted in communities, the new report suggests.

Detecting water theft should get easier as more advanced monitoring systems and sensors are developed, but for now a coordinated effort from governments, regulators and communities is needed to put an end to the scandal of half the world's water being stolen, the researchers say.

"Consistent with earlier research, the case studies clearly support the importance of well-resourced (financial and human) enforcement and compliance monitoring especially in the remoter parts of delivery systems, to increase the probability of detection and prosecution as an important driver of theft reduction," conclude the study authors.

The research has been published in Nature Sustainability.