The Apple Watch Series 3 is here... and it's cellular. This means you can use web-connected apps on your watch when you're away from the companion iPhone, opening a whole new world of Apple Music-powered runs.

But adding cellular capabilities to a smartwatch is not without its downsides. Aside from the effects on battery life, you will now have yet another greedy data sucker to worry about. So in this article we discuss the way the Apple Watch Series 3 will work with your data plan, and how to minimise data usage on the device.

The basics

First up, let's explain how cellular and data plans and all that jazz works with the Apple Watch Series 3.

To use cellular features on the Series 3 you need to sign up with one of the small number of providers who are able to offer watch plans in each launch country. In the UK that means EE - which, according to the company, is "the only network with the technology in place to offer Apple Watch Series 3 Cellular capability in the UK".

(You will also need to be using an iPhone 6, iPhone 6 Plus, iPhone SE or later handset.)

You can buy the watch from EE on a 24-month unlimited-data contract, which will set you back £25 a month plus an upfront charge of anything from zero to £160, depending on which model you want. EE has told us that "No 'fair usage' data limit is in place", so data isn't going to be an issue.

Alternatively, you can buy the watch from somewhere else (such as Apple), paying £329 or more for the device up front, and then add it to the EE plan your phone is on. This will be free for the first six months, with unlimited date, but thereafter will cost £5 a month for 10GB.

Note that EE does not offer roaming on its Apple Watch Series 3 plans, and that call minutes and texts are taken from your phone's allowance (although the company stressed that "the majority of SIM Only and Pay Monthly plans from EE have unlimited calls and texts".

EE answers questions related to the Apple Watch Series 3 on its website.

How to save data on Apple Watch Series 3

When does the watch use its own data, and when does it use the phone's data?

If your watch and phone are within Bluetooth range (and connected - so both must have Bluetooth enabled) then they will both use the phone's data.

But once you break the link between the two devices, either by moving them more than roughly 10m apart or by breaking the link by turning off Bluetooth. (Either way, you'll be able to tell that the Apple Watch has disconnected from its iPhone because a red icon will appear at the top of the screen.)

If you've been thinking it will be possible to 'share' data in the opposite direction - using the watch as a hotspot for the phone if the latter device is approaching its data limit - then EE has advised us that this will not be possible.

Keep on top of your data limit

You can keep track of your data use and limit by logging into your EE account online, or by using the My EE app for mobile. The app has one section for the phone and another for the watch.

There's no way to check your data usage on the watch itself.

EE has also told us: "Customers will receive an alert to their phone/watch when they have used 80 percent and 100 percent of their watch's data allowance, with a link to add more data if needed."

Use a data-monitoring app

There are a few Apple Watch apps that are designed to monitor data usage on themselves and their companion iPhone.

The way this all works is likely to change significantly when the Series 3 arrives so we would not recommend paying for such an app at this point. But there are some free options that are worth a try, such as DataFlow.

Settings - a general tip

Something that cannot properly be assessed until the Apple Watch Series 3 and watchOS 4 come out is the range of settings that will allow you to minimise data usage.

For example, it's possible on the iPhone's Apple Music app to select or deselect High Quality Streaming - a decision which depends largely on how tight your data plan is looking at the present moment.

We've not seen how this works on the Apple Watch Series 3 but if you are given the option, it would be worth making sacrifices in terms of quality (especially when running, where quality tends to be subsumed beneath volume and bass content) in order to minimise data usage.

Many Apple Watch apps, both first- and third-party, will offer ways to limit data usage. Check carefully to see what the options are for the apps you like, and consider tightening data usage if you find you are approaching your limit.

How to save data on Apple Watch Series 3

Apple Music

Talking of which, Apple Music was one of the highest-profile 'use cases' that Apple discussed on stage - which makes sense, because setting up and syncing a playlist of songs on the Apple Watch is a pain, and streaming from Apple's extensive music library while running (with no iPhone) is far more appealing.

But in terms of data you should beware. Like most streaming services Apple Music uses a lot of data. If you're approaching your monthly data limit, Apple Music may be a good app to steer clear of - or maybe it would be worth taking the phone with you just this once.

Airplane Mode

Having cellular on your Apple Watch Series 3 is going to call for a new way of thinking.

In the past, the watch was just an accessory. When it was within Bluetooth range of your phone, it would pull in notifications and updates from online as appropriate, using the phone's web connection, but when it wasn't, it reverted to being a self-contained fitness tracker with no online capabilities.

Now, whenever you're away from your phone, your watch is going to be pulling down its own data, checking for updates and issuing notifications off its own bat. And that's not necessarily a good thing.

Assuming you're on an limited-data plan, and particularly if you're approaching your monthly data limit, it's worth switching on Airplane Mode from time to time - when you're away from your phone and don't mind being off the grid. When you can wait until you get back from the run before picking up texts or the latest cricket score.

(Admittedly, there are downsides to this: Airplane Mode turns off GPS too. A better option would be a simple cellular toggle in Control Centre, something we hope to discover when we try out watchOS 4 on the Series 3.)

Of course, doing this more than occasionally rather undermines the reason for buying the Series 3 in the first place.