Yorkshire Water has justified an “unwelcome” increase in customers’ water bills by saying the rise will help pay for a £376 million programme of improvements to services.

Bills will go up on April 1, which will mean the average customer will spend £1.75 per month or £21 in total more than they did last year, an increase of 6.1 per cent.

A high inflation rate of 5.2 per cent is driving rises in water prices nationally, according to industry regulator Ofwat which approved the water companies’ budgets.

The average Yorkshire Water bill will rise to £361, compared to a national average of £376, the Bradford-based water company said.

The investment scheme includes almost £5 million to improve drinking water quality in Bradford by upgrading the Chellow Heights and Graincliffe Water Treatment Works.

There will also be a new approach to moorland management above Keighley to improve the quality of water and £120 million to improve waste water treatment facilities and the company’s sewer network.

Richard Flint, Yorkshire Water’s chief executive, said: “Whilst the majority of this rise is down to inflation, the remainder of the increase will be used to fund our ongoing investment in Yorkshire, which in 2012/13 will be £376 million.

“Whilst we do many things very well, we know there are things we can do better, such as driving down pollution incidents and bursts on our network of underground pipes.

“All this investment will deliver huge benefits, from cleaner rivers and bathing waters and more robust and reliable drinking water supplies, through to a reduction in the number of homes and businesses affected by flooding from sewers during times of exceptional rainfall.”

Ofwat chief executive officer Regina Finn said: “We understand that any bill rise is unwelcome, particularly in tough economic times. Inflation feeds through into water bills, and this is driving these rises.

“We will make sure customers get value for money. Companies are investing £22 billion by 2015 – more than £935 for every property in England and Wales.”

Dame Yve Buckland, chairman of the Consumer Council for Water, said it would work with companies and Ofwat to ensure future water prices are “acceptable and affordable”.

Barbara Leech, of the Consumer Council for Water, said: “This is a difficult time financially for many people and these rises will add to their problems but we encourage anyone finding it difficult to pay to contact the company immediately.”