Drinking Water

Water Quality

Ambient Water Quality Criteria for Colour in British Columbia: Technical Appendix

3. Drinking Water

3.1 Water Treatment

The major mechanism for removal of dissolved coloured substances such as humic and fulvic acids is the coagulation/sedimentation process (National Health and Welfare 1993). In British Columbia, very few water purveyors apply treatment more than disinfection. Organics removal by coagulation has been found to be optimal at pH 4 to 6. Removal of organic material by aluminum and iron salts is effective with removal efficiencies varying from 55 to 90% between source waters (Reckhow and Singer 1990). In order to prevent the formation of trihalomethanes (THMs), the initial point of chlorine application should follow the coagulation/sedimentation process; reductions in THM production of up to 75% have been reported by such a change in process (National Health and Welfare 1993). Oxidation of THM precursors by chemical oxidants other than chlorine (e.g., hydrogen peroxide, ozone, UV radiation) are possible methods of THM control. Alternatively, disinfecting agents other than chlorine may be used to avoid the formation of THMs. Removal of THM precursors by activated carbon has had limited success because of early breakthrough problems (Symons et al. 1982). Special treatment for THM control after formation usually involves air stripping and adsorption (Symons et al. 1982). Note that the removal of other colouring agents such as iron, copper, surfactants and dyes may require different treatment techniques. For example, iron removal usually consists of oxidation by chlorine, potassium permanganate or ozone followed by liquid/solid separation (National Health and Welfare 1993).

Suspended particulates that contribute to apparent colour are generally removed during the pre-treatment step usually by a combination of coarse and fine screens, micro-strainers and/or simple gravity settling (National Health and Welfare 1993).

3.2 Effects

Few toxicity studies of colouring agents such as humic and fulvic acids have been undertaken. The few studies that have been conducted indicate that organic colouring agents are not toxic at the levels that could occur in drinking water. For example, male rats supplied with soil fulvic acid for up to 90 days at levels of 10, 100 and 1000 mg/L showed no significant changes in body weight, intake rates, organ/body weight ratios or tissue histology (Health Canada 1996). Little information is available on the toxicities of metals and their humate complexes (Health Canada 1996).

Limits for colour in drinking water are generally based on aesthetic considerations. Research into perception of water quality tends to support the view that the public uses many factors in judging water quality, but that visual factors predominate. In particular, consumers find water with low clarity or a yellowish hue to be objectionable (Smith and Davies-Colley 1992; Smith et al. 1991). Levels of colour above 15 mg/L Pt in a glass of water can be detected by most people (Health Canada 1996).

Although colour per se represents an aesthetic problem in water supplies, potential harm to humans can arise due to the reaction between humic and fulvic acids and chlorine to form THMs, trichloroacetic acid, dichloroacetic acid, haloketones and haloacetonitriles (Reckhow and Singer 1990; Rook 1977). Many of these compounds are probable carcinogens to humans or have been shown to be mutagenic (Health Canada 1996; Reckhow and Singer 1990). Reckhow and Singer (1990) observed that the average yield of THMs in drinking waters of seven US cities was 52.2 g/mg total organic carbon. In cities with high organic carbon concentrations in the raw water (greater than or equal to 15 mg/L), concentrations of THMs were observed in the low mg/L range (Reckhow and Singer 1990).

3.3 Literature Criteria

Most countries have established criteria for true colour in drinking water based on aesthetic considerations using the Hazen scale. For example, the true colour criterion derived by Health Canada, Quebec, Australia and the World Health Organization is 15 mg/L Pt because this is the level at which most people can detect colour in a glass of water (Ministere de l'environement du Quebec 1992; WHO 1983; Health Canada 1996; NH & MRC and AWRC 1987; Australia 1992). Most countries recommended criteria for turbidity and suspended solids to protect drinking water from the constituents of apparent colour. No criteria for apparent colour to protect drinking water were found in the world literature.

3.4 Proposed Criteria

The aesthetic water quality criterion for true colour is 15 mg/L Pt. This criterion should not be exceeded at any time, but only applies to systems in which background colour is less than 15 mg/L Pt and the water does not require treatment beyond disinfection.

3.5 Rationale

The criterion for true colour is set at 15 mg/L Pt to ensure that consumers whose drinking water is aesthetically unpleasing do not seek alternative, possibly unsafe, sources of drinking water. It also recognizes that most water purveyors in British Columbia do not treat water supplies beyond disinfection. The provision of drinking water at or below this limit will also guard against interferences by colour in treatment water processes and analytical procedures (Health Canada 1996). The removal of excess colour prior to chlorination will also reduce the production of THMs and other substances that complex to humates at low levels. Given that criteria for turbidity and suspended solids are a better means to address inputs of suspended matter that cause coloration of water supplies and that where available drinking water treatment effectively removes suspended particulates, no criterion for apparent colour is required.


	Water Quality Ambient Water Quality Criteria for Colour in British Columbia: Technical Appendix 3. Drinking Water 3.1 Water Treatment The major mechanism for removal of dissolved coloured substances such as humic and fulvic acids is the coagulation/sedimentation process (National Health and Welfare 1993). In British Columbia, very few water purveyors apply treatment more than disinfection. Organics removal by coagulation has been found to be optimal at pH 4 to 6. Removal of organic material by aluminum and iron salts is effective with removal efficiencies varying from 55 to 90% between source waters (Reckhow and Singer 1990). In order to prevent the formation of trihalomethanes (THMs), the initial point of chlorine application should follow the coagulation/sedimentation process; reductions in THM production of up to 75% have been reported by such a change in process (National Health and Welfare 1993). Oxidation of THM precursors by chemical oxidants other than chlorine (e.g., hydrogen peroxide, ozone, UV radiation) are possible methods of THM control. Alternatively, disinfecting agents other than chlorine may be used to avoid the formation of THMs. Removal of THM precursors by activated carbon has had limited success because of early breakthrough problems (Symons et al. 1982). Special treatment for THM control after formation usually involves air stripping and adsorption (Symons et al. 1982). Note that the removal of other colouring agents such as iron, copper, surfactants and dyes may require different treatment techniques. For example, iron removal usually consists of oxidation by chlorine, potassium permanganate or ozone followed by liquid/solid separation (National Health and Welfare 1993). Suspended particulates that contribute to apparent colour are generally removed during the pre-treatment step usually by a combination of coarse and fine screens, micro-strainers and/or simple gravity settling (National Health and Welfare 1993). *3.2 Effects* Few toxicity studies of colouring agents such as humic and fulvic acids have been undertaken. The few studies that have been conducted indicate that organic colouring agents are not toxic at the levels that could occur in drinking water. For example, male rats supplied with soil fulvic acid for up to 90 days at levels of 10, 100 and 1000 mg/L showed no significant changes in body weight, intake rates, organ/body weight ratios or tissue histology (Health Canada 1996). Little information is available on the toxicities of metals and their humate complexes (Health Canada 1996). Limits for colour in drinking water are generally based on aesthetic considerations. Research into perception of water quality tends to support the view that the public uses many factors in judging water quality, but that visual factors predominate. In particular, consumers find water with low clarity or a yellowish hue to be objectionable (Smith and Davies-Colley 1992; Smith et al. 1991). Levels of colour above 15 mg/L Pt in a glass of water can be detected by most people (Health Canada 1996). Although colour per se represents an aesthetic problem in water supplies, potential harm to humans can arise due to the reaction between humic and fulvic acids and chlorine to form THMs, trichloroacetic acid, dichloroacetic acid, haloketones and haloacetonitriles (Reckhow and Singer 1990; Rook 1977). Many of these compounds are probable carcinogens to humans or have been shown to be mutagenic (Health Canada 1996; Reckhow and Singer 1990). Reckhow and Singer (1990) observed that the average yield of THMs in drinking waters of seven US cities was 52.2 g/mg total organic carbon. In cities with high organic carbon concentrations in the raw water (greater than or equal to 15 mg/L), concentrations of THMs were observed in the low mg/L range (Reckhow and Singer 1990). 3.3 Literature Criteria Most countries have established criteria for true colour in drinking water based on aesthetic considerations using the Hazen scale. For example, the true colour criterion derived by Health Canada, Quebec, Australia and the World Health Organization is 15 mg/L Pt because this is the level at which most people can detect colour in a glass of water (Ministere de l'environement du Quebec 1992; WHO 1983; Health Canada 1996; NH & MRC and AWRC 1987; Australia 1992). Most countries recommended criteria for turbidity and suspended solids to protect drinking water from the constituents of apparent colour. No criteria for apparent colour to protect drinking water were found in the world literature. *3.4 Proposed Criteria* The aesthetic water quality criterion for true colour is 15 mg/L Pt. This criterion should not be exceeded at any time, but only applies to systems in which background colour is less than 15 mg/L Pt and the water does not require treatment beyond disinfection. *3.5 Rationale* The criterion for true colour is set at 15 mg/L Pt to ensure that consumers whose drinking water is aesthetically unpleasing do not seek alternative, possibly unsafe, sources of drinking water. It also recognizes that most water purveyors in British Columbia do not treat water supplies beyond disinfection. The provision of drinking water at or below this limit will also guard against interferences by colour in treatment water processes and analytical procedures (Health Canada 1996). The removal of excess colour prior to chlorination will also reduce the production of THMs and other substances that complex to humates at low levels. Given that criteria for turbidity and suspended solids are a better means to address inputs of suspended matter that cause coloration of water supplies and that where available drinking water treatment effectively removes suspended particulates, no criterion for apparent colour is required.