Testing Rainwater for Potability
For checking that rainwater collected is safe to drink
Taking a Sample | Guides and Supporting Information | Contact us Today
About this Testing
Testing rainwater is covered by our Routine Water profile, of particular interest are the following parameters:
|
Test |
Typical Range |
NZDWS 2005 Maximum Acceptable Value (MAV) |
Comment |
|
pH |
5.7 |
7.0-8.5 |
The pH of pure rainwater is a slightly acidic 5.7 unless it is being stored in a concrete water tank which can bring the pH up to over 7. |
|
Copper |
N/A |
2 mg/L |
Can be leached from copper piping by acidic rain water |
|
Zinc |
N/A |
1.5 mg/L |
From galvanised roofing materials |
|
Lead |
N/A |
0.01 mg/L |
From lead flashing and nail heads on house rooves |
|
EColi |
5-20 (untreated) |
<1 mpn/100mL |
Usually detected due to faecal matter from birds, cats and possums |
|
Approx TDS |
10-20mg/L |
<1000 mg/L |
Sea spray contributes to dissolved constituents in rainwater. |
Rainwater itself is very suitable for drinking, having a pH of approximately 5.7 and being low in dissolved salts and micro-biological contamination. Unfortunately it is often contaminated by the collection methods (mostly house roofs) with:
|
Contaminant |
Source |
|
Micro-organisms |
Faecal matter of birds, cats and other mammals deposited on the roof |
|
Tastes and odours |
Rotting vegetation trapped in gutters, pipes and holding tank |
|
Pesticides |
Spray drift and atmospheric deposition, although concentrations are likely to be very low |
The pH of 5.7, while not harmful to humans (table wine has a pH of approximately 3.5), can be corrosive to metal pipes and fixtures. For these reasons, together with variations in supply and quality, it is not recommended as a source of drinking water for communities.
Before any testing is carried out, gutters, downpipes and lines to the holding tanks should be thoroughly cleaned. Gutter protection (allows water into the gutter but prevents leaves and other debris from entering), and first flush diverters (diverts the initial flush of rainwater to waste), should also be installed. A pH adjustment system is recommended to raise the pH to 7.0-8.5, as well as a disinfection system to kill the micro-organisms (e.g. UV filter). A charcoal filter could also be used to remove spray residues and any lingering tastes and odours. Once your treatment system is installed, testing should be carried out to determine whether it is effective.
Taking a Sample
In terms of where to sample, it is very important to have a clear idea of what information you are trying to obtain. For example, if you are only interested in the quality of water coming out of your kitchen tap, then the sampling should take place there. However, if you have installed treatment and you want to find out how effective it is, then you may want to take 2 samples - one from the tank (pre-treatment) and one from the kitchen tap (post-treatment), and 2 sampling kits will be needed.
When taking the sample, it is very important to follow the instructions provided, especially for the Ecoli test. This requires a sterile container (square plastic 400mL) and the tap needs to be sterilised to make sure that no contamination occurs. Also note that we need the samples back with 24 hours and less than 10°C, otherwise the results will not be valid. For clients who are not within easy driving distance from Hamilton or Christchurch, we suggest taking your sample in the early afternoon and sending it overnight to the laboratory.
Unsure about the correct container to use to submit a sample? Consult our container guide
Sampling equipment
Request a Routine Water Kit from the Laboratory by contacting one of the client service managers below. The routine water kit contains 3 sample containers which are all required for one test, i.e. they should all be filled from the same sampling point, not from 3 different points.
Guides and Supporting Information
Contact
Contact us today on 07 858 2000 (North Island) or 03 377 7176 (South Island) or click below for the contact details of:
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