Simple chemical tests give a rough picture of water: red cabbage extract or turmeric paper shows whether the water is acidic, near neutral or alkaline against the 6.5-8.5 pH range given for drinking water, a soap test shows how hard it is, and a chlorine test kit reads treatment. No home test detects heavy metals, pesticides, arsenic, fuel or most industrial chemicals, so a source with a risk of those must be avoided and not just tested.
Part of Community Water Testing
Simple chemical tests are the low-cost checks of a water supply’s basic chemistry: acidity or alkalinity, hardness, iron and the chlorine left after treatment, done with household materials or a small kit.
Rough Chemistry Is Worth Checking, And Worth Not Over-Trusting
The community water testing page gives a drinking-water pH range of 6.5 to 8.5 and two home indicators. These tests matter for practical reasons: acidic water eats metal pipe and fittings, very alkaline water makes chlorine disinfect poorly (above about pH 8, the chlorine effect falls; see Dosing Calculation), and both change the taste. The tests do not measure safety. I recall that the WHO sets no health-based pH guideline, treating 6.5-8.5 as an operating range, so a result outside it is a reason to look at corrosion and disinfection and not by itself a reason to condemn the water.
What You Need
- Red cabbage and a pan, or turmeric powder and plain paper
- White vinegar and baking soda for comparison solutions
- Clear cups or jars, all the same size
- Soap (a plain bar) and a clear bottle with a lid, for hardness
- A chlorine test kit (Chlorine Residual)
Method: Make A Colour Ladder First
Step 1: Red cabbage indicator. Chop red cabbage finely and boil it in water for 15 minutes. Strain; the purple liquid is the indicator. It spoils in a day or two, so make it fresh.
Step 2: Make a ladder. In a row of cups of clean (boiled, cooled) water, make an acid end with a little vinegar and weaker versions of it, a neutral cup of plain water, and an alkaline end with a little baking soda and weaker versions of it. Add the same number of drops of indicator to each.
Step 3: Add the same drops to your sample and match its colour to the ladder.
Step 4: Read the bands. The carrier’s guide is red or pink for acidic (below pH 6), purple for neutral (pH 6.5-7.5), green for alkaline (pH 8 and above) and yellow for very alkaline (above pH 10). Use these only as a first guide. As I recall, red cabbage reaches yellow only at a much higher pH, nearer 12, so trust your own ladder over the number printed beside a colour.
Step 5: Turmeric strips. Soak turmeric powder in water to make a yellow solution, dip paper strips and dry them. A strip turns reddish-brown in alkaline water, pH above 8.
Step 6: Hardness. Shake a measured amount of water with a fixed bit of soap in a clear bottle. Soft water gives lasting lather; hard water gives scum and little lather. Compare with a soft reference such as rainwater (Hardness and Iron).
Step 7: Chlorine. Use a test kit; the smell is not a measure.
Worked Example: Building The Ladder
Dilute in steps of ten to cover a wide range. Take 1 teaspoon of vinegar in 100 ml of water, then 10 ml of that in 90 ml of water (a tenfold dilution), then 10 ml of that in 90 ml (a hundredfold). Do the same with baking soda. The seven cups, strong acid, mild acid, faint acid, plain water, faint base, mild base, strong base, show the colours your cabbage gives. A sample whose colour matches the plain-water cup is near neutral; one that matches the first cup is strongly acidic. The ladder shows order, not numbers, so a sample “between the faint-acid and plain-water cups” is close to neutral, and one “beyond the strong-acid cup” is far from it and worth tracing to a cause.
What These Tests Cannot Do
The tests do not see heavy metals, pesticides, nitrates, arsenic, fluoride, fuel or most industrial chemicals. These may be present in clear, odourless, neutral water. Sedimentation, sand filtration and chlorination do not reliably remove them (Treatment Selection). If a source lies downstream of mining, old industry, fuel storage or sprayed fields, change the source.
Common Mistakes
- Reading the colour without a ladder. Lighting and the extract’s strength change the colours.
- Using old extract. It spoils.
- Treating a normal pH as a clean bill of health. It is one number about one property.
- Treating hard water as unsafe. It is mostly a scaling and taste matter.
Safety
Keep test materials apart from drinking water
Vinegar and baking soda are harmless alone, but never mix vinegar or any acid with bleach or pool chlorine: the mixture releases chlorine gas. Do not drink the test samples or ladder cups, and label them. Wash the containers before returning them to food use.
What’s Next
- Learn next: Chlorine Residual — the most important chemical test for treated water
- Combine with: Hardness and Iron — mineral content in detail