Low Water Pressure in Metro Denver: What to Check and What Fixes It

Is it low pressure or low flow?

The two feel the same in the shower, but they are different problems. Pressure is the force pushing water into the house, measured in pounds per square inch (psi). Flow is how much water actually gets through the pipe in a given time. A house can have perfectly normal pressure at the street and still get a weak trickle if the pipe carrying it is undersized or choked with scale.

Denver Water makes this point directly: in homes built in the 1930s and earlier, it says the usual issue is a reduction in flow rate that people read as poor pressure. Its Customer Care line (303-893-2444) can tell you the tap size and install date for your address and the pressure at that location, which is a useful starting point before anyone opens a wall.

A ten-minute check before you call anyone

1. Map the problem. Open the cold side at the kitchen, a bathroom sink, a tub and an outside hose bib. Is it one fixture, one bathroom, only hot water, or everything?
2. Read the pressure. A screw-on gauge from a hardware store fits a hose bib. With nothing else running, the reading is your static pressure. Write it down, then open a tub faucet and watch how far it drops.
3. Look at the valves. Make sure the main shutoff and any valve near the water heater are fully open. A valve left half closed after a repair is a common and easy fix.
4. Check for a hidden leak. With every fixture off, watch the meter's leak indicator. If it moves, water is going somewhere.
5. Ask a neighbor. If the people next door lost pressure at the same time, the cause is probably on the utility side.

Why so many older Denver houses have weak flow

Denver Water's own history of service lines explains a lot. It says homes built before 1900 often have half-inch taps and lead service lines, later homes often have 5/8-inch taps with galvanized steel lines, and three-quarter-inch copper lines became standard in the 1950s and 60s. Over time, minerals build up on the inside of lead and galvanized pipe, narrowing it and roughening the surface. The utility says that buildup does not pose a health threat, but it does cut flow, and the older the pipe, the worse it gets.

That history matters because so much of the city's housing is not new. About 55.5% of Denver homes were built before 1980, and the median year built is 1975. The same scale can form in galvanized pipe inside the house, which is why some owners replace the service line and still find the upstairs shower disappointing. In that case replacing the old indoor supply pipe is often the real fix.

If your line could be lead, contact Denver Water before you pay for anything. Its Lead Reduction Program replaces lead service lines with copper at no direct cost to the customer.

What does a pressure reducing valve do, and can it fail?

A pressure reducing valve (PRV) sits on the main line just inside the house and steps street pressure down to a safer level for fixtures and appliances. The Department of Energy's Building America Solution Center notes that municipal pressure can exceed 200 psi in places and that most plumbing codes require a PRV where supply pressure is above 80 psi. Not every home has one, and when the street pressure is moderate a PRV may not be needed.

When a PRV wears out, it can fail in either direction. A valve stuck partly closed starves the house. A valve that stops regulating lets pressure creep up, which shows up as banging pipes, running toilets and dripping relief valves. The same source points out that a PRV turns the plumbing into a closed system, where heated water has nowhere to expand, so a plumber replacing one should also look at how thermal expansion is handled at the water heater.

Could a leak be stealing your pressure?

A break on the line between the meter and the house can bleed off enough water to make every fixture feel weak. Signs include a soft or unusually green strip of lawn, a meter that keeps moving with everything off, or a water bill that jumps without explanation. A plumber who does leak detection with acoustic and pressure testing can usually pinpoint it before any digging.

Who pays depends on where the leak sits, and the dividing line moves from one utility to the next:

• Denver Water: the property owner owns the service line from the main in the street into the house, along with the meter.
• Aurora Water: the city owns the line up to and including the meter pit, and the owner is responsible from the pit to the building. If you live in Aurora, that split decides who digs.
• City of Lakewood utility area: the city maintains the main, the line to the meter pit and the pit itself, and the owner maintains the line from the pit to the house. Other districts inside Lakewood may differ.
• City of Arvada: the city owns the line to the meter pit and the owner owns it from the pit to the foundation.

If the leak is on your side, a service line repair or replacement is the next step. When the meter moves but the yard is dry, the water may be escaping under the floor instead; our guide to the warning signs of a slab leak covers what to look for.

Only the hot water is weak

If cold is fine everywhere and hot is weak everywhere, the problem is almost always at or near the water heater. Check that the cold inlet valve on top of the tank is fully open. Sediment can also collect in the tank and in the outlet fittings, and Denver Water describes its water as harder in the southern part of its system and in winter, which speeds up scale in heaters and fixtures. A plumber handling water heater service in Denver can flush the tank and inspect the dip tube and fittings. If the tank is old and full of scale, read when to repair a water heater and when to replace it before spending on parts.

One fixture is weak

Unscrew the aerator on the faucet spout or the head of the shower and look for grit or white scale. Soaking it in vinegar often restores full flow. If the aerator is clean, the cartridge inside a single-handle faucet or the shower valve can be partly clogged. A faucet repair visit usually covers a cartridge swap. Homes that keep fighting scale sometimes add a water softener sized to the household, though Denver's water is soft to moderately hard and many homes do fine without one.

When the problem is on the utility side

A sudden drop that hits the whole block points to the water system, not your plumbing. Denver Water's emergency line is 303-628-6801. Other cities run their own lines: Aurora Water's after-hours number is 303-739-6772, and Arvada lists 720-898-7070 for main breaks. Call the utility before booking a plumber when water is surfacing in the street or several neighbors are affected.

Homes on private wells

In foothill towns and on the eastern plains, plenty of homes pump their own water. Low pressure there usually traces to the pressure switch, a waterlogged pressure tank, a clogged filter or a pump that is wearing out. Those are different repairs from anything above, and a plumber who handles well pump problems in Evergreen and similar mountain areas will start at the tank and switch.

What the fixes tend to involve

Cleaning an aerator or opening a valve costs nothing. Replacing a PRV or a cartridge is a modest repair. Replacing a service line or repiping a house is a much larger job that Denver Water itself calls very costly, and its suggested alternative is living with the flow and adding water-conserving fixtures. In Denver, water service work on single-family and duplex homes is a quick permit issued online through Community Planning and Development. For a sense of how plumbers price work around the metro, see what a plumber costs in Denver, and ask for a written quote before work starts.