A few labeled locations can be more useful in a leak than a folder full of product brochures.
The short answer
Mark the service entry, main shutoff, water heater, fixture shutoffs, appliances, and any sump pump on a simple household sketch. Separate supply water from drainage. The illustration on this site is conceptual; your property may have a different layout, equipment, ownership boundary, or water source.
What to notice
The first mark: the shutoff
Locate the valve you have been told controls the house supply. Record how it is reached and what it actually controls. A shutoff behind storage or a locked door may not be available during a leak. Do not force an old valve to test a theory. Have a qualified provider explain safe operation and whether a valve needs repair or replacement.
Give each room a small record
For kitchens, bathrooms, and laundry areas, note the visible fixture valves and appliance connections. Include the date of a previous leak or replacement. A phone photo can help you remember a connection, but it should not contain access codes or other private details. Label rooms in plain language that another household member would understand.
Add equipment and ownership boundaries
Record the water-heater model, pump location, and any pressure-control or leak-monitoring device you can identify. Ask the utility or provider where responsibility changes between the public system and property plumbing. A meter, service-line inventory, or exterior valve is not an invitation to operate utility equipment. Store the map where occupants can find it.
One useful question
Should I draw every pipe?
No. A useful household map locates controls and equipment. Concealed routes should remain unknown unless reliable records establish them. Drawing an imagined pipe path can mislead a later repair conversation. Mark uncertainty openly and ask the provider to update the sketch after verified work.