Finding and fixing leaks is one of our top priorities, but with the resources available to us we can’t fix them all. We’re working on the issue, but it won’t happen overnight – and summer is almost here. The risk of a water shortage this summer and tighter water restrictions is real, and the situation may shift quickly.

To ensure there’s enough water to go around for the necessities, we need everyone to do their bit. Water restrictions help people understand how they can best save water at their place, and when to do so. If people follow the restrictions, it reduces the chance of moving to higher levels.

Water restrictions are enforced through council bylaws. Wellington Water recommend the level of restrictions for our council owners to implement.

Here’s where you can see what water restrictions apply in your area and what this means for you.

Over the past two summers, there has been a real risk of tighter water restrictions – but they’ve been narrowly avoided thanks to substantial and unusual rainfall in summer because of ex-tropical cyclones Dovi and Gabrielle. We can’t assume that this will happen again. El Niño conditions are forecast, and we’re expecting a hotter, drier summer than the previous two.

This combination of increasing leaks, population growth, above average water use, and forecast El Niño conditions all increase the risk of tighter water restrictions.

Our modelling shows that if we have an average summer – meaning no significant rainfall – our councils will have to put tighter water restrictions in place to reduce the risk of an acute water shortage.

This comes down to water demand and supply capacity. Water use in the metropolitan Wellington region is at an all-time high. Leaks are increasing due to the water network being old, population growth is driving up the demand for water and Wellingtonian’s simply use more water than comparable regions.

We also have a finite amount of water we can treat and supply on any given day. This includes a “buffer” that allows for varying levels in daily water usage, unplanned outages, or planned maintenance work. However, the increase in leaks in the network means the available ‘buffer’ is becoming increasingly tight.

In winter, when there is plenty of rain and the river levels are healthy, we can supply up to about 220 million litres of water per day.

But in summer, when it’s hot and dry and river levels drop, this can go down to about 170 million litres of water per day.

170 million litres might sound like a lot, but Wellington is using and losing more water than ever before – often getting up to 205 million litres per day in summer!

You can see that those numbers don’t work. When demand is higher than the available supply from the rivers and aquifer, then we have to dip into the water stored in the storage lakes. But this stored water is precious and is critical for getting through a long dry period, and in summer it’s harder to refill the lakes. So over time, they get lower and lower, leaving Wellington with less and less water stored and available until next winter.

Rain helps us fill the storage lakes during winter, so we can use it during summer when river levels drop. But this storage has a limit – once it’s full, it’s full, and more rain in winter doesn’t change that.

We’re only able to take water from the rivers when they’re above a certain water level. But heavy rain can be just as bad as not enough! When there’s short bursts of heavy rain, it can fill rivers with dirt, sticks and debris. This makes it harder to treat (make safe to drink) and risks blocking the pipe and tunnels that supply the treatment plants. This means that sudden downpours are much less helpful than they seem.

Currently, the two storage lakes (the Macaskill Lakes, at Te Mārua) store up to 3.35 billion litres of water – enough to supplement supply for 2 – 3 months in summer. Wellington Water and our council owners are progressing plans to increase the available water storage.

Wellington’s daily water supply has a limit, as the treatment plants can only supply so much. If demand exceeds what the treatment plants can supply there’s a risk that the water levels in the storage reservoirs across the region are drawn down too low, causing water quality issues and in an extreme scenario even depressurising areas of the network. This can be dangerous as it increases the risk of contamination of drinking water, and boil water notices may need to be issued to stop people getting sick.

This means we have to be very careful to manage the daily water supply and demand, and don’t use too much. That’s where water restrictions come in. They help everyone understand how they can best manage their personal water use, so there’s enough to go round for the necessities.

Level 1 splits outdoor water use between odd and even houses, to spread the load of daily water demand. This means people can water their gardens regularly without everyone using a lot of water all at once. It also reduces waste by restricting watering to the morning and evening, when water is less likely to evaporate in the heat of the day.

Level 2 makes sure people are watering their gardens only when they really need to, with no sprinklers or irrigation systems, and only watering gardens by hand.

Level 3 comes into play when we need to take serious action, and all residential outdoor water use must be stopped. We know that people put a lot of hard mahi and love into their gardens, so consider using grey water to water your garden – just not your vegetables, or any plants you’re planning on eating.

Level 4 means we’re in a significant water shortage. On top of stopping all outdoor water use, we must reduce indoor use. This could include 2-minute showers and reducing laundry to one load per person, per week.