Begin with the problem in front of you
Describe what you see before choosing a cause or a product. A faucet dripping from its outlet raises a different first question from water appearing beneath the sink. A smell only at a hot-water tap is a different starting point from the same smell at several hot and cold taps.
The leaky faucet guide and rotten-egg smell guide show how the location of a symptom changes the next check without establishing an exact cause on its own.
Use the evidence that actually changes the answer
A guide should move from a usable observation to the next piece of evidence. Different questions need different kinds of evidence.
- Observe
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Where and when does it happen?
Note the fixture, location, timing, and whether the problem appears in one place or throughout the home.
- Measure
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What number changes the choice?
Keep the actual measurement and its reference points. The toilet rough-in guide uses the finished wall and bolt centerline rather than a guessed nominal label.
- Identify
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Which specific item or result do you have?
An exact replacement part needs identifying markings and manufacturer fit information. A water result needs the reported value, units, and sampling context.
Keep the boundary of an answer visible
An observation can narrow a search without proving the diagnosis. A photo of a faucet may help locate the leak but cannot by itself identify the installed cartridge. An odor may suggest where to check but cannot by itself establish a health risk or a treatment system.
When the source is hidden, the water cannot be controlled, or a result needs laboratory interpretation, the next step may be professional or local-authority help. A guide should say so before suggesting a purchase.
Choose the next guide from what you know now
Follow the link that matches your present question. A diagnostic guide may lead to a measurement, an exact-part guide, a testing guide, or a question to bring to a professional. Gather the evidence that changes the choice before buying a part or treatment.