A Welsh council has denied spending about £70,000 a year on bottled water, saying it was just an estimate.
A Freedom of Information Act request was issued to councils
That would put Carmarthenshire 20th in a bottled water expenditure list after a survey of most Welsh and English councils for the BBC's Panorama.
The council said its estimated figures to the BBC may include other costs.
The programme, Bottled Water - Who Needs It? found councils had a bill totalling more than £5m, although some, such as Merthyr, spent nothing on it.
If Carmarthenshire's figures were accurate, that would mean it spent more on bottled water than any other council in Wales.
The programme, to be broadcast on BBC1 on Monday, investigates the monetary and environmental costs of bottled water consumption in the UK.
The programme made a Freedom of Information request to many of the councils in England and Wales to find out how much they had spent on bottled water in the previous financial year.
The total figure came to more than £5m with Hampshire topping the table. It spent £141,215 on bottled water between November 2006 and October 2007.
WELSH COUNCIL BOTTLED WATER SPENDING
Vale of Glamorgan: £30,042.33
Neath Port Talbot: £26,605.48
Rhondda Cynon Taf: £12,906.50
Blaenau Gwent: £7,410.60
Merthyr Tydfil: £0
SOURCE: Panorama. NB: The figures for some Welsh councils were not available
In its reply to Panorama, Carmarthenshire said its procurement service had produced the estimate of £70,000.
It reported that the approximate number of bottles consumed per year was 14,000, at an average cost of £4.95 per 19-litre bottle.
In a statement, the council said it was not possible to calculate the exact amount it spent on bottled water because it was not allocated a specific cost code in its records.
A spokesperson said it was recorded in the council's general ledger against headings such as "administrative and office equipment", "stationery/general" and "other hired and contracted services".
"To isolate truly accurate figures for expenditure on bottled water would require a manual search of many hundreds of invoices in relation to every transaction," the council said in a statement.
"It would be necessary to look not only at invoices received from known suppliers of bottled water and extract the data, but also to identify any other companies that may have supplied water to the authority."
Some of the councils asked for the information admitted the figures given might not be accurate because their accounts did not differentiate between payments for bottled water supplies and payment for other supplies.
Conwy declined to give Panorama a figure for this reason.
Caerphilly claimed that the cost of complying with the request would exceed the limit of £450 for local government.
UK Environment Minister Phil Woolas has described the amount the country spends on bottled water as "morally unacceptable" and is urging people to use tapped water instead.
Panorama: Bottled Water - Who Needs It? will be shown on BBC1 at 2030 GMT on Monday, 18 February.