Recycled water sampling technique

Safety Procedures

There are potential health hazards associated with the use of recycled water. The risk of diseases arises from the pathogens that may be present in raw sewage which are removed to varying degrees during treatment processes.

Persons engaged in any operation involving recycled water (including sampling) should ensure they:

• Wash hands well with soap before eating, drinking or smoking, and when finished working with wastewater or the recycled water.

• Do not consume food or drink, and do not smoke while working with wastewater or recycled water.

• Wear / use suitable clothing and safety equipment appropriate to the task being undertaken.

• Clothing and equipment should be washed after use

• Do not wash hands with or drink wastewater or recycled water, and avoid inhalation of spray.

On site pH Measurement

The relative concentration of chlorine species in water is affected by pH. Increase in pH requires a greater chlorine contact time to achieve the desired pathogen log inactivation by chlorine.

The measurement of pH can be done by using pH probes or pH indicator strips.

pH probes

pH probes are suitable if they are correctly maintained and regularly calibrated (monthly). Calibration/maintenance procedures of the pH probes need to be included in the Recycled Water Quality Management Plan to ensure validity and reliability of the instrument measurement. Instruments without proper maintenance and calibration will give poor readings.

pH indicator strips

Strips are a quick, simple and cost effective option to record pH measurement. Strips are ready for immediate use and are maintenance free. Strips cover different pH ranges from the universal ranges 0 to 14 or 1 to 10 to more specific ranges. If used please ensure

• The strips must cover at least the 6-10 pH range. 
• Test strips that have two colour pads per pH level are preferred over single tone dispenser reels, single tone test strips, or other indicator papers. This assists staff with colour blindness to accurately read the pH value.
• pH values taken in-situ shall be recorded on the lab request form 
• Only use test strips before expiration date
• Hi heat or humidity could shorten expected shelf life of the strips. Follow manufacturer ‘s storage recommendations.
• Follow manufacturer’s instructions for their use

On site Chlorine Measurement

Where schemes are chlorinated it is important that the level of chlorine is measured prior to sampling. A sufficient chlorine dose must be added to allow for the chlorine demand reactions to occur, and to ensure that there is an adequate free chlorine residual available to disinfect the recycled water effectively. If the reading shows the free chlorine level is low this should be investigated and restored before sampling is carried out. 

Chlorine dosing systems, ideally with flow-proportional automatic dosing and feedback loops should be used to achieve target chlorine residual and provide rapid responses to any changes in flow and water quality. Chlorine sensors should be used to continuously measure hypochlorous acid (HOCl) and temperature in recycled water to determine free chlorine concentration.

On site chlorine measurement can be done using the DPD (diethyl paraphenylene diamine) liquid reagent. There are different test kits and instruments commercially available for analysing the chlorine residual. Examples include but are not limited to colour-wheel test kits, comparators, digital colorimeters and photometers. Calibration/maintenance procedures of the instruments need to be included in the Recycled Water Quality Management Plan to ensure validity and reliability of the instrument measurement. Instruments without proper maintenance and calibration will give poor free chorine readings.

Tap Samples

1. Turn the on tap full and allow the water to run to waste for 2 minutes. This flushes the interior of the nozzle and discharges stagnant water from the pipe.
2. Turn off the tap and sterilise the spout by heating it with a blow lamp, gas torch or by igniting a piece of cotton wool soaked in methylated spirits until any water in the tap boils
3. Cool the tap by allowing the water to run to waste for a few seconds.
4. Adjust the tap to deliver a gentle stream of water.
5. Clearly label the bottle. (See Sample Bottle Labelling for further details).
6. Hold the bottle in one hand and remove the screw cap with the other. Hold the cap open side down and keep it close to the bottle.
7. Fill the bottle to within 5mm from the top by holding it under the tap taking care to avoid splashing.
8. Carefully replace the cap.
9. Place the bottle into a biohazard bag and seal.

Documentation

The Water Examination Laboratory requires all samples to be accompanied by a correctly filled out WB (blue) form:

• Make sure that the pH and the level of chlorine are recorded on the form.
• Write on sample collection report: copy to Water Unit, Department of Health Western Australia. 

Site Code Number

A site code number is a computerised identification number that must identify all samples and accompanying documentation. Site codes are only assigned by the Department of Health. The basic site code numbers have:

• Three-digit Wastewater Treatment Plant (WWTP) ID 
• Two-digit Primary Recipient ID
• One-digit Secondary Recipient ID
• Two digit sample type code ID as indicated below

WWTP	Primary recipient	Secondary recipient	Sample type ID
AAX/	XX	X	XX

For more information regarding site codes please contact the Water Unit.

Table 1: Recycled water sampling requirements for common analysed parameters

Parameter (units)	Volume required	Type of bottle ** ^	Preservation	Maximum sample holding time
Turbidity(NTUs)	250 mL Fill bottle just below shoulder	Plastic or glass	Refrigerate at 1–4 °C Do not freeze	24 hours
pH (pH units)	125 mL Fill bottle to the top to exclude air Sample must be free of air bubbles	Plastic. Bottle cap must have a teflon liner	Refrigerate at 1–4 °C Do not freeze	6 hours In situ test is preferable to
Chlorine Residual (mg/L)	500 mL	Plastic or glass	Monitored in-situ by on-line sensors	Immediate analysis is preferable Maximum holding time is 5 minutes Keep sample out of direct sunlight
BOD (mg/L)	1 L Fill bottle to the top to exclude air. Sample must be free of air bubbles	Plastic or glass brown (amber)	Refrigerate at 1–4 °C Store in the dark Do not freeze	Analyse as soon as possible after collection or within 24 hours if sample is refrigerated at 1-4°C
Suspended Solids (mg/L)	1 L Fill to the shoulder of bottle	Plastic	Refrigerate at 1–4 °C Do not freeze	Analyse as soon as possible after collection or within 24 hours if sample is refrigerated at 1-4 °C Do not hold samples longer than 7 days
Total Nitrogen (mg/L)	200 mL Fill bottle just below shoulder	Plastic	Refrigerate at 1–4 °C or freeze Store in the dark	Analyse within 24 hours if sample is kept refrigerated at 1- 4 °C Analyse within 30 days if kept frozen below -20 °C Alternative holding time is 7 days at 4 °C
Total Phosphorus (mg/L)	200 mL Fill bottle just below shoulder	Plastic	Refrigerate at 1–4 °C or freeze Store in the dark	Immediate analysis is preferable Analyse within 24 hours if sample is kept refrigerated at 1-4 °C Analyse within 30 days if kept frozen below -20 °C Alternative holding time is 7 days at 4 °C
Microbiological (including coliphage) (cfu/100mL)	100 mL per microbial analysis 200 mL is required for the AS for coliforms and E.coli, and total plate count Fill to below shoulder of bottle	Sterilised plastic or glass Use new precleaned sterilised bottles	Store in the dark Refrigerate at 1–4 °C	24 hours Immediate analysis is preferable

Notes to accompany Table 1

• Appropriate plastic bottles are high-density polyethylene (HDPE), polypropylene, polycarbonate or a fluoropolymer (e.g. Teflon).
• Whenever possible plastic is preferred for occupational health and safety issues.
• NTU: nephelometric turbidity units
• cfu: coliform forming units
• ** Ensure sample bottle is pre-rinsed three times with sample water (3 × 20 mL) before final collection.
• ^ Use new pre-cleaned bottles
• Samples for TN and TP determination can be collected in the same 250 mL container.
• All parameters in the table are unfiltered samples for laboratory analysis

More information

• Water Unit, Environmental Health Directorate
  Telephone: 9222 2000
  Postal address: Department of Health, PO Box 8172, Perth Business Centre WA 6849
  Email: ehinfo@health.wa.gov.au