Report No FR0191

P H Jago and J Easton

Mar 1991



To validate through national and international comparative trials the procedure developed at WRc for measuring the growth potential of water in distribution. To develop the WRc method further, in accordance with internationally agreed recommendations. To investigate the development of simpler and less expensive methods.


Assimilable Organic Carbon (AOC) is one of the causes of regrowth of micro-organisms in distribution systems, such regrowths can have adverse effects on the taste, odour and colour of potable water. The WRc method of measuring AOC is already assisting several water utilities, but its value compared with other European methods which measure the Biodegradable Dissolved Organic Carbon (BDOC) is unclear, and the degree of inter-laboratory variation in AOC measurements needs to be quantified. Most existing techniques of AOC measurement are costly in manpower and materials, and the WRc method also requires the use of specialised, expensive instrumentation and reagents. In consequence, greater acceptance of AOC measurement depends on the development of cheaper and simpler methods of analysis.


  1. National 'round-robin' trials of AOC methods have shown that different laboratories and methods can give similar results now that some standardisation has been introduced.

  2. Differing international approaches to the concept of biodegradable carbon in water have resulted in the measurement of two parameters AOC and BDOC.

  3. It is now clear that although arising from a common concept these two parameters are quite distinct and have different applications. AOC is a measure of the regrowth potential of a water in distribution, whereas BDOC is a measure of the organic carbon that can potentially be biologically oxidised during water treatment.

  4. BDOC and AOC are time consuming to measure and so far efforts to simplify the analyses have been unsuccessful.

  5. Other novel techniques developed in other laboratories for AOC and BDOC measurement appear worthy of further evaluation.


Where possible, existing AOC and BDOC methods should be standardised by the adoption of a common approach, and further inter-laboratory comparisons should be carried out. A choice of methods would now appear to be available, AOC to measure the regrowth potential of a water entering distribution, and BDOC as a measure of the potential biodegradability of a water during water treatment. Cheaper and simpler techniques need to be developed if the assay of AOC is to be used routinely by all water utilities. Novel methods will require evaluation.


This report presents the results of two 'round-robin' trials of AOC and BDOC measurement techniques carried out in Europe and North America. In addition, trials of a simpler alternative method is discussed, and a brief description of papers presented at WQTC, San Diego November 1990 on the subject of AOC and BDOC.

Copies of the Report are available from FWR, price 25.00 less 20% to FWR Members