Welsh households could save up to £25 a year off their water bills from 2020 to 2025 under plans put forward by regulator Ofwat.
The watchdog said its upcoming price review would be tough on companies and ensure customers can look forward to "lower bills, improved services, reduced leakage and more help for the most vulnerable".
Under the plans, which set limits on the prices that customers in England and Wales will pay for water between 2020 and 2025, Ofwat said it is proposing to set the so-called cost of capital that has a direct bearing on bills at a record low of 2.4%.
It said this could see customers save between £15 and £25 a year on average from 2020.
The plans give water companies less room to charge customers based on the costs of raising debt or equity.
This comes after Ofwat drew harsh criticism from the Public Accounts Committee last year for consistently overestimating companies' costs when setting price limits - leading to higher bills for customers.
Ofwat said it will also for the first time see help for vulnerable customers included as an "explicit part" of the price review, with water companies required to draw up and deliver plans to identify and help those in need. The regulator said it wants suppliers to "go the extra mile" and take firmer action on tackling leaks.
In its most stretching target yet, it wants firms to save 170 billion litres of water a year - enough to meet the annual needs of 3.1 million people. .