The conventional global image of the UK is very much ‘the land of the long grey cloud’, as they say in New Zealand, where the drizzle is only interrupted by the rain.

And yet, as the long, hot summer of 2022 drew to a close Thames Water, the water utility that encompasses both London and Slough, revealed that it was conducting an investigation into the water usage of data centers across its region amid concern that they are simply consuming too much.

That might sound absurd in the rain-soaked autumns and winters that followed in both 2022 and 2023, but the finger of blame for water shortages in parts of the UK was being pointed at data centers. But, across the world, data center water usage issues are becoming almost as big a political issues as, well, data center power issues.

Unfortunately, it’s hard to say with complete accuracy whether such accusations are fair, because estimating data center water usage is even more challenging than estimating data center power usage, which until now has had far more attention.

However, a 2021 paper by Lawrence Berkeley National Laboratory research scientist Dr. Arman Shehabi – the same scientist who led earlier research estimating data center power usage – indicates that the data center industry is one of the top-10 commercial users of water in the US.

Moreover, unlike other major water-using industries, Shehabi claimed, the data center sector tends to use mains water in cooling, adding to pressure on potable water supplies.

Switching to low water consumption mechanical cooling doesn’t help either, as this only increases water usage at the power station, which has to generate the extra power necessary to run the equipment, both Shehabi and Jon Pettitt, chief commercial officer at Excool, point out.

In other words, whatever way a data center uses to air-cool its IT hardware, water usage is involved somewhere along the line – a lot of it. “In almost all types of power generation, water is used. So when it comes to cooling, water consumption and power consumption always go hand-in-hand,” says Pettitt.

In other words, data centers trying to lower their water consumption only push it to the power station to generate the extra electricity to power the mechanical cooling, with the added disadvantage of electrical losses between power generation and data center averaging around 14 percent.

All this, of course, strikes at the heart of the ‘water usage effectiveness’ (WUE) measure, but there are various ways in which data center cooling systems can both use less water and less power, while reducing reliance on the public water supply, too.

Harvest for the data center

There is more than one way of saving – or, more accurately, better managing – water. For example, data center operators can use rain water harvesting instead of mains water.

“You’ve got to start off by working out the annual load, and what you need in terms of water – 150 cubic meters? 200 cubic meters? – and what that means in terms of rainwater harvesting: when do you need it most, how much will you need, and when can you harvest it?” asks Pettitt.

An apparently straightforward concept therefore requires quite an intricate formula to ensure that a sufficient amount of water is captured at the right times of the year, and organizations that rely on rainwater harvesting obviously need to err on the side of caution to ensure that they’re not caught short during, say, an unexpected heat wave.

In other words, several years of rain water figures need to be examined, and the system and storage tanks set-up in expectation of somewhere around the minimum rainfall you can reasonably expect.

However, while rain water obviously needs to be filtered, it is relatively clean (and probably makes a better cup of tea than London tap water). It’s therefore eminently suitable for data center use. “Rain water is fairly soft and fairly clean, but it does need to be handled the right way,” says Pettitt.

Having a supply of water onsite, rather than relying on mains water, is increasingly important in places like California, for instance, which are subject to serious forest fires. As a result, fire services are legally entitled to commandeer water supplies to fight the fires, cutting off businesses and households in the process, in addition to powers enabling them to shut off power, too. While data centers insure themselves with backup generators against the loss of power, how many take similar measures to guarantee an ongoing water supply?

“If you’re running a critical facility, you’ve got to plan for every eventuality, so Excool has mechanical cooling technology inside the Excool Zero unit enabling it to run for periods of time almost completely water-free until water services are restored,” says Pettitt. “But it also carries a 24-hour tank. We fill the tank up then use the water from the tank from the bottom and fill it from the top, so the tank is always draining and there’s no risk of stagnant water developing.

“However, as soon as there is any issue with the water supply, the unit goes into what’s called ‘water saving mode’, which balances the conventional water-based cooling with mechanical cooling to minimise water usage accordingly. At any one time, you should have enough water in the tank sufficient for 24-hours of cooling,” says Pettitt.

And the system, of course, can be filled with filtered, harvested rainwater.

Unless you’re based in Singapore.

“In Singapore, when it rains, the rainwater legally belongs to the Singaporean government. You’re not allowed to capture it without being subject to a tax on what you capture,” says Pettitt.

However, in Singapore there are two sources of water supplies available – potable water piped into everyone’s home and ‘new’ water. While the new water is not recommended for adding, say, to a Glenfiddich 50 year old single malt scotch, it is not only reasonably clean, but also soft, making it usable for the purpose of data center cooling systems.

Indeed, soft, well-filtered water has become absolutely essential since the phase-out of lead-based solder because silver solder, which has replaced it, is more volatile to many of the contaminants that can be imported into the data center from outside air and water if the cooling system’s filters are not as good as they should be.

Intelligent design

At the same time, says Pettitt, there’s a good reason why Excool calls its latest indirect evaporative cooling system the Excool Zero: because the level of water consumption required to produce the same level of cooling has been radically slashed.

“We've moved from using, five years ago, maybe swimming pools worth of water across our heat exchangers to now using just bucketfuls or cupfuls, but getting a very similar efficiency as a result of how we control the use of the water within the system,” says Pettitt.

“The key to this massive improvement in water usage is the heat exchanger,” says Pettitt – especially the hybrid heat exchanger that Excool manufactures in-house to its own particular standards for its own products.

“So we have a non-metallic heat exchanger that's hermetically sealed. That enables neither air nor moisture to pass between the two extremes. We manufacture our own heat exchanger, and we test every single heat exchanger to ensure it's 100 percent right,” says Pettitt.

The materials in the heat exchangers are vacuum formed at the factory. “Then we place every single plate on a light box and inspect it for any tiny imperfection. That might just be where the material looks to be slightly thinner than it ought to be and, if we do find any that fall short of our standards it gets rejected,” says Pettitt.

Between 500 and 1,000 heat exchanger sheets roll of the production line every day, and each and every one gets a light box inspection.

Furthermore, being non-metallic – unlike the sheets typically used in a conventional heat exchanger – ensures there is no rust or corrosion, while the filtering ensures that there are no blockages. “We’ve also changed our heat exchanger design to a counterflow, which has enabled us to shrink our unit considerably in terms of its size and footprint,” says Pettitt. “This also makes it easier and quicker to install on site, at a reduced unit cost, too.”

On top of this, the introduction of even more advanced machine learning to the Excool control software helps to fine-tune both water- and power-management of the devices.

This intelligent control can also be used to fine-tune costs, as well as usage, by, for example, ramping up mechanical cooling at night when power prices are low and using more water (and therefore less power) for cooling during the day. “Or, it could be based on outside conditions, how much water is in the internal tank, and even account for whether it’s also running off an external water tank, too,” says Pettitt.

In particularly water-stressed parts of the world, not just being able to fine-tune to such a degree, but having the cooling system’s control software assisting is a significant benefit.

Return to normal

Back in the UK, meanwhile, after two consecutive rain-soaked winters Thames Water should no longer be short of water for some time to come. For data centers, though, technology such as rain water harvesting will no doubt remain attractive, if only to demonstrate how much the sector does in terms of sustainability.

But the data center water challenges in many parts of the world are unlikely to abate anywhere near as easily as Thames Water’s. Hence, the ongoing challenge of providers and operators not just to slash both water and power usage of cooling systems, but to offer much greater flexibility and intelligence in how they’re used, too.

Click here to find out more about Excool’s flexible, efficient, low-water usage cooling solutions