Water filtration + microbial growth comparison

Where to buy & price

Just examples of where to look and roughly what to expect to pay, get everything from wherever works for you, at whatever price you find.

Plastic bottle (reused, cut in half), sand/gravel free or ~KSh 50, activated charcoal (aquarium charcoal, pet shop) ~KSh 100–200. Also requires a second set of homemade agar plates: unflavored gelatin ~KSh 100–150, bouillon cube (Royco) ~KSh 10–20, two small clear containers reused or bought cheaply.

Cold storage / timing

The comparison agar plates need the same treatment as the standalone agar-plate experiment: refrigerate ~30 minutes to set faster (or 1–2 hours at room temperature), then store cool and use within 2–3 days.

Reagents & materials required

Procedure, step by step

1. 1

   Cut the bottom off a plastic bottle and turn it upside down to use as a filter funnel.

2. 2

   Layer filter materials inside from bottom to top: a piece of cloth or cotton at the very bottom to hold everything in, then a layer of activated charcoal, then a layer of sand, then a layer of small gravel or pebbles on top.

3. 3

   Collect a sample of "dirty" water (pond water, or tap water mixed with a bit of soil) and pour half of it through your filter, collecting the filtered water in a clean cup below. Keep the other half unfiltered as your control.

4. 4

   Make your own nutrient agar plates: dissolve 1 bouillon cube in 1 cup of hot water, then stir in 2–3 tablespoons of unflavored gelatin until fully dissolved.

5. 5

   Pour the warm mixture into two small, clean, clear containers to a depth of about 1cm each, then let them cool and set, refrigerate for about 30 minutes, or leave at room temperature for 1–2 hours, until firm.

6. 6

   Once set, drop or swab a small sample of the filtered water onto one plate and the unfiltered water onto the other, labeling each clearly.

7. 7

   Cover each plate loosely and incubate both somewhere warm for 2–3 days.

8. 8

   Check daily without opening the containers, and compare the amount of visible microbial growth (spots, cloudy patches) between the filtered and unfiltered samples.

9. 9

   Once you're done comparing, dispose of both plates by sealing them in a bag before throwing away.