A councillor has suggested Perth and Kinross Council should consider the number of bottoms rather than houses polluting Loch Leven.
A council committee last week gave the nod to revised guidance to protect the Kinross-shire loch - designated as a Special Protection Area.
The changes have been made as a result of problems with Loch Leven's water quality due to phosphorus and nitrogen entering the loch from manmade sources.
Perth and Kinross Council's Finance and Resources Committee was recommended to approve the update - when it met on June 15 - to support the implementation of PKC's Local Development Plan (LDP).
The aim is to ensure phosphorus levels in the loch do not increase as a result of waste water from new developments in the Loch Leven area. The guidance sets out requirements for phosphorus mitigation for private wastewater systems.
The report - put before councillors last week - said the Kinross-shire Local Committee raised concerns over "a discord between the LDP reducing the housing land requirement in Kinross-shire to protect Loch Leven, and the housing numbers on allocated sites invariably being approved for higher numbers than identified in the plan".
The Kinross-shire Local Committee was content with the revised guidance subject to this and "continued issues with combined sewers where the storm drains overflow during periods of heavy rainfall releasing sewerage into the catchment" being addressed when the next version of the LDP is prepared.
Blairgowrie and Glens SNP councillor Tom McEwan - who lives next to a Perthshire loch with similar issues - said he was "scratching his head" over the number of houses being a factor.
He said: "I thought in relation to phosphate, it's the amount of phosphate produced by a house i.e. the number of people/bottoms in that house that is the actual marker.
"So one four-bedroomed house could have the same phosphate production as three two-bedroomed houses could have. And actually the important thing is the number of people that would be expected to live in any said development not the said number of houses that is important in relation to phosphate production."
A council officer told Cllr McEwan that was a "correct assumption" and they had reallocated some of the housing land requirement from Kinross-shire to Perth.
Development plan team leader Brenda Murray said: "When we were preparing the plan we did realise there is this issue in relation to the Kinross-shire area specifically. So it was felt it would be prudent to look to allocate some of the housing land requirement for the Kinross-shire area outwith that housing market area into the Perth housing market area to try and alleviate any potential issues arising from that aspect.
"It was taking account of the sensitivities in relation to the loch itself so that was why we chose to take that approach."
Planning officer Robert Wills acknowledged it was a "valid point" and added: "Obviously within the plan it's quite difficult to manage numbers of people. It came about by looking at the environmental assessment of the previous development plan and looking at how much areas were constrained by designations and environmentally sensitive areas. The Kinross-shire housing market area was a lot more constrained by environmental considerations than other areas.
"That was why we took the decision - as a precaution - to move 10 per cent of the housing land to another area."
The revised guidance was approved.
