重压之下的供水产销差危机
供水产销差不仅仅包括管网输送过程中水的物理漏损（也称漏失），也包括由于仪表设备，计量统计方法，非法偷水等因素造成的表观漏损。每年都有大量的水资源由于漏损被浪费掉，而水务公司也会因为产销差遭受严重的经济损失。在亚洲城市，平均每天都会有6000万立方米的水漏失，这一数量相当于2.3亿人口的供水需求；而全球城市每年的产销差损失更是达到了惊人的140亿美元。今天的疏失将加剧明天的困扰。未来的水资源形势要求水务公司重视供水产销差问题，一方面寻找漏损控制的技术突破，同时也完善漏损的检测评估标准、计量方法和绩效审计机制，追求更加科学的管理方式。
Counting what's invisible
Tracking down non-revenue water (NRW) involves a complex process that continues to evolve. But non-revenue water represents a mix of not only leaks in the distribution system but also leaks of data and information from challenges with meter reading and billing, as well as theft from illegal connections.
And it’s not just water that vanishes; with every drop leaked or lost, you also see disappear the expensive chemicals, energy, carbon footprint and labour that went into treating the water in the first place. To prepare for an outside audit, or conduct one internally, the American Water Works Association (AWWA) and the International Water Association (IWA) help break down all water into three categories:
1. Unbilled Authorised Consumption
Water consumption that publicpolicy exempts from paying rates. Think water used for fire-fighting, drinkingfountains or water used to flush mains
2. Apparent or 'Commercial' Losses
Water theft, data errors andmetering inaccuracies. Think slow, inaccurate or misread meters, andunreported, unauthorised usage from hydrants and mains
3. Real or Physical Losses
Leaks in the system, everywhere fromstorage tanks to transmission and distribution mains, to pre-meter leaks inservice connections
The goal of an audit and proactive steps that follow “is not to get to zero water loss,” explains Steve Cavanaugh, Chair of the Outreach Subcommittee of the American Water Works Association Committee on Water Loss Control. “Rather, it is to get to the economic level of water loss considering the current circumstances.” That level is not static. “Environmental, political, regulatory, public relations and other drivers are constantly evolving so the utility develops business practices that are sustaining,” adds Cavanaugh.
Abolish the paradox of NRW percentage
It’s always easier to reprimand others than to confess. As freshwater grows scarce or costly, utilities turn first outward, to demand management. They warn of leaky pipes–on the customer side of the meter–and impose fines or ‘name and shame’ campaigns until clients fix them. But just try to ask those same utilities to confess how much water is leaking on the district’s side of the meter. Many have no idea. Fewer may even keep track. Those who do tend to use an old, random and flawed metric–a percentage of total supply–that makes little sense now, if ever it did.
Let’s assume a utility manager with 10,000 accounts annually treats and pumps 1 billion litres of water to customers, but only collects revenues on 825 million litres. So she flips over an envelope, pulls out her pencil, subtracts bills paid from flows provided, divides total volume by the difference, and voila, jots down “17.5 percent NRW”. That’s a fast calculation. It’s also a meaningless metric.
Every water loss specialist The Source spoke with regards the percentage figure with contempt. Most want governments to ban, censor or expunge it from all discourse. They see the non-revenue water (NRW) percentage as: “misleading”, “flattering”, “physically inconsistent”, “mathematically flawed”, and even “institutionally dangerous”.
Why such scorn? For starters, it actually masks losses. The above utility could grow 5 percent each year (annually adding 500 new accounts and 5 million more litres), and after 10 years push its NRW figure down to 11.6 percent without fixing one leak. Far from integrity, it merely increases the denominator.
There’s also the problem of shifting ratios. The NRW percentage figure will vary dramatically by season, weather conditions, or time of day. After midnight, in a wet year or during winter overall systemic demand falls. As a result, the NRW percentage will appear to have increased as pressure forces water out of joints, pinholes and cracks more intensively. Conversely, on hot summer afternoons in a dry year, percentages will appear to decrease when demand rises. Both mask the actual impact of the physical leaks.
A utility leaking 100,000 litres a day from 15 kilometres of pipes in the summer may have an Infrastructure Leakage Index of 3, or three times worse than optimal ©Alliance for Water Efficiency
Not only do leaks linger, the losses may increase due to a third paradox: pressure as a growing utility adds 50 percent more accounts and water each decade, the utility may increase pressure from 10m (1 bar) to 20m (2bar) and thus increase leakage through the same holes by 100 percent.
“We are finally making headway in eliminating the percentage of system input volume parameter,” says Steve Cavanaugh. Like others, he advances a new “comprehensive methodology with a suite of metrics that matter with water loss shown in terms of volume, value and validity”.
The new industry standard offers a more exacting and revealing water balance methodology, with a custom-tailored Infrastructure Leakage Index (ILI). This metric takes into account each system’s unique length and size of plumbing, storage, accounts, climate, usage and geography, to develop the optimal level that is technically achievable by each utility.
“The ILI is the ratio between the minimum achievable leakage and the actual level of leakage,” said Roland Liemberger, the NRW Management Specialist at Miya . “A perfect system therefore has an ILI of 1 (actual=minimum) but in low and middle income countries systems have ILIs of 50, 100 or even more!”
This water balance metric adds up in dramatic ways. When Reinhard Sturm’s team audited 17 California water utilities, it found non-revenue water to be 1.6 to 6.6 times higher than optimum levels, and projected that an economic recovery of just 40 percent would annually save half a trillion litres per year.
Today’s denial will intensify tomorrow’s pain
Several forces are converging to nudge reform. Rapidly growing cities need to combat scarcity. Heads of state push for water security. Industry groups demand comparable accountability standards. Civic groups sueutilities for casual or creative bookkeeping. Bond rating agencies punish dithering. And contractors offer fees based on proven recovery.
'Water utilities are under game-changing pressures today from internal and external forces,” says Steve Cavanaugh, Chair of the Outreach Subcommittee of the American Water Works Association Committee on Water Loss Control. “Most managers don’t know what they don’t know, but across the industry, people are starting to wake up and decide how to get their hands around this issue. We are finally reaching a tipping point.”
Today’s denial will intensify tomorrow’s pain. To save millions of litres of water a day you must publicly acknowledge years of wasting it. But if managers don’t raise NRW proactively, outsiders will. “For those who continue to ignore the signs or postpone programmes, the costs of inaction include natural resource depletion, increased regulatory mandates (both funded and unfunded), and, eventually, public pressure from concerned consumers,” said Steve Cavanaugh “The old business model simply doesn’t work in the face of today’s business, environmental and regulatory climate.”