Drinking water and new developments

On average, we each use 150 litres of water a day, or one tonne per week. If housebuilding targets of 300,000 homes per year are to be met, and based on an average household occupancy of 2.36 people, we will need to redirect an additional 36m tonnes of drinking water to new homes each year.

Unfortunately, even the most developed nations can struggle with an oversupply of floodwater and an undersupply of drinking water - problems which will be exacerbated as climate change increases the frequency of flooding and droughts and the need for new homes puts pressure on existing water supplies. 

Planning and Development InSite spoke to Matt Hare about the extent to which the planning sector can resolve these issues. Matt is a Planning partner at Carter Jonas in Cambridge, officially the UK’s driest city. Cambridgeshire also has one of the fastest growing populations: of the five new towns initiated in England in the last decade, two were in Cambridgeshire and the county's population is forecast to grow by 21.7% between 2020 and 2041.

And so it is unsurprising that Matt recently succeeded in gaining planning consent on behalf of Cambridge Water for a new drinking water reservoir in Knapwell, which was necessary to serve the growing population including the significant expansion of Cambourne. Perhaps more surprising is that the Council’s development plan did not include any policies expressly supporting or identifying the need for this infrastructure despite the allocation of substantial housing growth in the area.

‘Without adequate new drinking water infrastructure, growth would be restricted,’ says Matt. ‘Growth can give rise to various water-related impacts on existing communities, be that drinking water related or otherwise. Just seven miles from Cambourne, the village of Longstanton recently suffered ecological damage when nearby a development of 10,000 homes allegedly caused a drop in the ground water level and many ponds dried up, to the detriment of local wildlife. 

‘In simple terms the water authorities have a statutory duty to provide drinking water to serve new development. In many instances the areas administered by the country’s various water authorities, but they extend across multiple local authority boundaries. Take Anglian Water for example, which covers an area of land that stretches from Grimbsy and Basildon. Clearly efficient operation requires an excellent strategic oversight of the anticipated growth pressures across the area – a significant challenge when the area includes in excess of fifty local authorities. This is a challenge that is made all the harder since the abolition of the regional tier of plan-making and the somewhat volatile plan-making system that currently prevails.

‘The challenge for water authorities is further compounded by the way in which funding for infrastructure projects is controlled by OFWAT and is reviewed only on a five-year basis. In other words, it can be difficult for the water authorities to quickly change their infrastructure planning to address significant changes in local circumstances.

‘There is a strong argument for cross-boundary working when it comes to the capture of rainwater for drinking water use. So much of such water simply makes its way into rivers and streams and eventually the ocean, naturally without any regard to administrative boundaries. If some of that water could be captured then it could be used to support population growth with reduced need to extract ground water – however it would be very difficult and would likely require significant investment across multiple local authority and water authority areas.

‘There are also obvious flood risk benefits to this sort of approach. A strategic system designed to capture more rainwater for drinking use would likely also be well positioned to deal with the increasingly frequent rainwater deluges that the country experiences.’

In this regard, is there also a development-level responsibility for a more efficient approach to water management in general? Significant innovations have been introduced elsewhere. In China, for example, thirty ‘sponge cities’ have successfully enabled storm water to be captured and stored thanks to permeable pavements, rain gardens, ponds and wetlands, and used in place of drinking water. 

Matt explains, ‘On a more modest scale, grey water recycling can be very effective. Carter Jonas carried out the masterplanning for Eddington, a new development on the edge of Cambridge, which has the UK’s largest site-wide water recycling system. A sustainable urban drainage system channels rainwater through blue and green roofs and swales, which is then collected and reused for washing machines and toilet flushing.

‘But there are reasons why Cambridge can’t adopt the same approach as China. Rainwater harvesting is expensive to implement and maintain, so significant levels of rainfall are required to justify the expense. And while permeable road surfaces have clear environmental benefits, they are currently more expensive and complex to maintain, and in many areas simply will not be adopted by the local highway authorities.

‘There is more we can do - and will be doing - to introduce permeable surfaces for flood mitigation purposes. Green areas are often naturally permeable, and a requirement of the Environment Act is for new developments to have a minimum 10% biodiversity net gain, which may result in an increase in green spaces. 

‘But while the Environment Act might help in a small way to resolve the problem, the other proposed legislative changes are a concern, specifically proposals to ‘streamline’ the plan-making process which could restrict the ability to plan for utilities and add to the already difficult job that water authorities face when dealing with disparate Local Plans’

Clearly drinking water requirements must be planned through the strategic planning process prior to the development of new homes going ahead: whatever the future of the Local Plan process, planning must remain proactive, not reactive, if it is to ensure that drinking water capacity does not impact upon growth, and vice versa.