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I have been working on a science project were I have built a water filter.

To prove that it works I would need to test if there are bacteria in a sample which has been treated vs a sample that hasn't been treated.

I really just need to know if there are bacteria not how many. I looking to do this at home.

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  • $\begingroup$ Put your filter on a nice and rich medium in a petri-dich and it will give you an idea of whether there are bacteria. Fitlering different amount of water will allow you to quantify. There are always potential bacteria you will not be able to grow on this specific medium and therefore it is pretty much impossible to really prove that something is completely sterile. $\endgroup$
    – Remi.b
    Mar 27, 2016 at 17:13
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    $\begingroup$ en.wikipedia.org/wiki/Bacteriological_water_analysis $\endgroup$
    – CKM
    Apr 2, 2016 at 14:36
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    $\begingroup$ There are many techniques. You should add some details to narrow down the question, which include- the available infrastructure, ease of experimentation, monetary budget, time required for analysis and other relevant information. $\endgroup$
    – WYSIWYG
    Apr 6, 2016 at 5:11

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There are many ways to do this. User Grb's answer is good but his method requires access to equipment.

If this is a highschool level project, you could make two Nutrient Agar petri plates. Spread 1 milliliter of unfiltered water on one and 1 milliliter of filtered water on the other. Make sure this is done in a sterile environment (using a Bunsen burner for example). The presence of colonies on your filtered plate would indicate that there are still bacteria in the filtered water.

You can also count the number of colonies on both plates. If there are less colonies on the plate with filtered water, your filter works to a certain extent. If the counts are identical, your filter does not work. If you use colony counts, make sure you repeat the experiment multiple times to obtain statistically rigorous result.

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IF you are looking at a much faster technique but don't mind spending a bit and have some research equipment access, there are ways by which bacterial contamination can be detected by measuring ATP (Adenosine tri-phosphate). See this research publication. There are commercial kits available which you can use: Here is one of them by Thermofisher.

Again, this is only if you have access to the research equipments and funds.

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