England is the only country in the world to have fully privatised its water and sewerage system. Almost 30 years on, it's not totally clear what we've gained: researchers say privatisation actually costs us £2.3 billion a year, summer brings water shortages to the south and east, and we still lose 20 percent of our water through leaks (by contrast, Phnom Penh in Cambodia loses 6.5 percent).

Fixing leaky infrastructure is the obvious way for companies to avoid a slap on the wrist and a fine from water regulator Ofwat. Unfortunately, this is also expensive, so last year one company decided to pursue an unlikely scapegoat: cannabis farms.

Thames Water attempted to obtain the address of every known cannabis farm in London from police, in a bid to calculate the amount of water lost to illicit consumption. The police refused to hand over the data, however, due to Data Protection legislation protecting individuals at the addresses where an offence had been recorded. When Thames Water made the request in December, it was six months away from censure by Ofwat. The company was fined the maximum penalty of £8.55 million in June for its "unacceptable" failure to improve a system that is currently losing 677 million litres of water a day – by far the highest rate of any water company in England and Wales.

Correspondence between Thames Water and London's Metropolitan Police service from December of 2016, revealed in a freedom of information request, outlined the company's bid for both the addresses of cannabis farms and the number of plants being cultivated at each address. "Thames Water are looking to understand the volume of water being used in our water supply area," read the letter to police. "This activity is currently unaccounted for and can affect several aspects of our operations and have negative financial impacts on customers," it added.

WATCH: High Society – How Weed Laws Are Failing the UK

The police refused to hand over the addresses, citing Data Protection legislation. "In this instance providing the address's [sic] of the locations where cannabis was being cultivated would allow for the identification of third parties," said the police response. "I have decided that disclosure of this information would breach principle one of the Data Protection Act, fair and lawful processing," the letter added. "My conclusion therefore is that disclosure would not be fair or lawful."

Thames Water provides water to Greater London, Surrey and other areas. It paid no corporation tax between 2011 to 2015, despite paying out over £1 billion in dividends from 2006 to 2015. Customers pay the third lowest average combined water and wastewater bill in England and Wales, according to Thames Water. Research by the University of Greenwich recently found that privatisation costs household about £100 a year more than if the utility companies had remained in state ownership.

According to Ofwat, about half of its customers are unmetered – meaning they pay an average water bill based on a number of variables. Water companies are unable to detect the water consumption of unmetered properties. "In terms of determining if an unmetered property is actually using more than the average, this isn't physically possible," Ofwat told VICE. According to Thames Water, "The difference between general water consumption and the amount billed is considered leakage." This essentially means that if Thames Water finds that more water is being used than they have calculated should be used (by adding together the metered usage and estimated unmetered usage), then they classify it as leakage.

But an alternative explanation could be excessive consumption: an unmetered or derelict property could be using more water than the average household for something water-intensive – like cannabis farming. Cannabis plants are water-hungry, and the Border Force now intercepts a smaller proportion of weed than regular police – which could be an indication that more is being grown domestically. According to police, cannabis production is booming. So could the cannabis industry account for all the "missing" water?

Unfortunately, the numbers didn't quite add up.

Photo: Owen Humphreys/PA Archive/PA Images

The figures the police gave to Thames Water show that there were 167 cannabis farms in London. If each had 25 plants, that's 4,175 total. If each required 22.7 litres of water a day, then that's about 94,000 litres total – 0.01 percent of the daily leakage. Of course, it's possible the farms were bigger than 25 plants each. The Office for National Statistics produces stats for the number of plants seized, and for the financial year 2015/16 it was 32,021 plants. But even that amount comes to 726,000 litres per day – or 0.1 percent of the total leakage. In other words, there would need to be 100 times as many cannabis farms in London as the police found for their water consumption to make a dent in Thames Water's leakage.

The company may have drawn the same conclusions, because in this year's Annual Report it says that it expects "to save 23.5 million litres of 'stolen' water over the next ten years, which would otherwise have been attributed to leakage". 23.5 million litres is just three percent of its total daily loss.

Thames Water told VICE: "In the absence of specific addresses where cannabis farms have been located, we've not been able to gain reliable information on the amount of water they use. A sudden increase in water consumption by a customer triggers a high bill alert notification. However, if the customer does not query the bill no further action is required.

"The difference between general water consumption and the amount billed is considered leakage. All leakage from our 20,000-mile network of water-pipes is investigated and, if an illegal connection is found, the matter is referred to our investigation team for action. We've not had any specific cases where our investigations uncovered a cannabis farm, but we would of course report this to the police if we did find one."

A spokesperson for Ofwat said: "Ofwat holds water companies to account if they do not deliver the commitments they have made to their customers on leakage. The failure by Thames Water to meet the leakage commitments it has made to its customers is unacceptable.