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  • 5th Dec 2022

Using behavioural science to redesign customer water bills

Interim results from a large-scale randomised control trial

This year featured the hottest summer on record in Britain. The Environment Agency declared drought status in many parts of the UK. In a time of increased water demand, reservoir levels are down, river flows are disrupted, and wildlife is at risk. To avoid such shortages in future, the average person’s daily water consumption needs to reduce from 140 litres to about 100-110 litres

However, change is a matter of policy and behaviour. Water shortages will require both improvements to supply infrastructure and reductions in consumption. The current state of affairs in the UK economy, however, presents a rare occasion when both policymaker and consumer incentives are firmly aligned. The government wants to avoid future droughts by reducing individual daily water consumption; consumers, worried about the cost of living crisis, want to keep their energy bills down. Enter BIT…

We’ve been thinking about the behavioural aspects of water efficiency and teamed up with Affinity Water and design agency Outré Creative to redesign customer bills using behavioural insights. Here, we summarise the approach we took and the results from the interim analysis. Whilst promising, we urge caution in generalising these results until the final analysis is completed in early 2023.  

A new, behaviourally designed bill  

Through an iterative co-creation process involving Affinity Water staff, customers and Outré Creative, we designed a new, behaviourally-informed, customer bill.

The new bill is more intuitive, useful, and motivating. Specific features included personalised feedback on water consumption using physical metaphors, the use of plain English (like litres, rather than m3), and social comparisons so people can gauge how much water they use compared to similar households in their local area. 

Old Bill vs New Bill –  Page 1 of each bill (full-page PDF version available at the links provided here) 

A large-scale field RCT to measure impact on water consumption 

To test the impact of these changes, we are conducting a large-scale field RCT with 850,000 metered Affinity Water customers. 

We randomly varied certain ‘modules’ within the new bill to identify the impact that specific elements have on water consumption. We also compared these versions of the new bill to a ‘fabricated control bill’ – a redesigned bill with behaviourally-informed modules stripped back or replaced by white space. The variations test: 

1. How we provide feedback to customers on their consumption: ‘per household’ consumption (PHC) vs ‘per capita’ consumption (PCC). Both of these styles of feedback help make a family’s water usage less abstract. The PCC style is more common in the water industry, but we hypothesised that the social comparisons to similar households (the PHC style) would outperform the traditional style by leveraging social norms. 

‘Per household’ consumption comparisons (left-hand side) versus ‘per capita’ consumption comparisons (right-hand side)

Download image here

2. What kind of encouragement we provide: an offer for a Home Water Efficiency Check, free water-saving gadgets or water-saving tips. 

Encouragement to book a home water efficiency check (left-hand side) versus tips (middle) versus encouragement to order gadgets (right-hand side) 

Download image here

Each bill’s exact content and module design depends on a customer’s situation. An example is the social comparisons to similar households. Approximately 50% of customers consume more than the ‘average similar household’ (left-hand image below). But the other 50% are better than average – and some of these customers are even better than efficient similar households (see the top-right and bottom-right images for examples of the feedback Affinity Water gave those groups of customers).  

Download image here

Affinity Water, BIT, and Outré Creative designed these modules carefully; for example, customers doing better than efficient similar households are explicitly thanked for their good work. 

Promising initial results 

Customers began to receive the new bill from July 2021, and we recently completed an interim analysis where we examined the first six months of consumption for the first ~40% of customers who received a redesigned bill. 

We will complete a final analysis once 100% of customers in the trial sample have 12 months of consumption under redesigned bills. We urge caution in generalising these results to the final analysis – there are various reasons they may be an underestimate or overestimate of the redesigned bill’s impact. 

With that said, these are the headline findings so far: 

Feedback that compared households’ consumption to similar households (i.e. PHC comparisons), in combination with either tips or an offer for water-saving gadgets, achieved a statistically significant 0.8%-0.9% reduction in consumption compared to the ‘fabricated control’.

Download image here

The effect is larger among customers who receive paper bills via post. It is small or non-existent for customers who receive their bills via email. We think this may be due to email customers paying less attention to their bills in general, and we and Affinity Water are working on ways to make email bills more salient. 

The redesign’s impact is larger among highconsuming customers. Comparing the control to the best-performing trial group (per-household social comparisons with gadget encouragement), we found the effect was largest for the third quartile of customers (50th-75th percentile based on pre-trial water consumption). We’ll explore this in more depth in the final analysis.

Download image here

The impact of small changes adds up

Although 1% savings from the redesign might seem small, when scaled across Affinity Water’s customer base, the total reduction adds up to a major impact. 

  • Total savings from the trial so far (comparing each trial group to consumption in the group that received the fabricated control bill), among the 293,000 customers in the interim analysis sample, is 87 million litres.
  • We expect that if Affinity Water switches all customers to the best-performing bill version (social comparisons + gadgets), total savings could be up to 880 million litres per year. 

With all that said, we await the final analysis in early 2023 to calculate final figures.