Sudden low water pressure in the whole house: diagnosis

What to do, in order

1. Check the main shutoff (at the meter or street side) — it should be fully open (handle in line with pipe). A knocked valve is the #1 cause.
2. Ask neighbors: if the whole street is weak, it's utility work — check your water company's outage page.
3. Test the pressure regulator (bell-shaped device at the main): attach a $10 gauge to an outdoor spigot. 40–60 PSI is normal; near-zero or 100+ means the regulator failed.
4. Look for leaks: water meter moving with all fixtures off = leak. Check the water bill for spikes.
5. If only hot water is weak: the water heater inlet/dip tube or shut-off is the suspect, not the house supply.

Red flags — stop and call a pro

• Meter spinning with everything off and no visible water — could be an underground/slab leak ( plumber with leak detection)
• Water hammer noises plus pressure swings — pressure spikes stress every joint in the house
• Sudden pressure LOSS with water pooling anywhere — burst line, shut the main

Prevention

Install a pressure gauge yearly check, replace the PRV every 10–15 years, and know where your main shutoff is before you need it at 2 AM.

This guide is maintained by the ee.ltd editorial team — reviewed for 2026. Browse all home repair guides or compare plumbing costs.

Related guides

• Water heater leaking from the bottom: what to do right now
• Clogged drain: when to plunge, snake, or call a pro
• Toilet keeps running: the 3 parts to check
• Find your main water shutoff before you need it at 2 AM

What this repair typically costs

• Water heater replacement cost guide
• Water heater repair cost guide
• Toilet installation cost guide
• Faucet replacement cost guide