Decide what you are filtering for
Filters are not general-purpose. A sediment filter catches particles. A carbon filter reduces chlorine taste and smell. Other media target specific contaminants. A filter that does not match your complaint will do little.
Start with a goal. Is it taste, cloudiness, scale or a particular concern from a water report? The goal decides the media. If the goal is scale, a filter is the wrong tool and the answer is conditioning or softening, which depends on hardness we cannot quote for you.
Test and read before you buy
- Read your provider's report. Utilities publish annual water quality reports for their supply.
- Test your tap. A lab test shows what is in the water at your house, including anything picked up in your pipes.
- Match the filter. Choose media and a flow rating that fit your findings and your household.
- Check the certifications. Look for independent certification for the contaminant you care about.
Not sure what your water needs? Call to talk it through.
Call (650) 860-1670What the install involves
A whole-house system goes on the main line after the shutoff and meter, before the branch to the water heater. The job means cutting into the main line, fitting bypass and shutoff valves and mounting the housing with room to change cartridges.
- Shut off the main and drain the line.
- Cut the pipe and install the unions and valves.
- Mount the housing level, with space below for cartridge changes.
- Reconnect, open slowly and check every joint.
- Flush the filter as the manufacturer directs.
Everything depends on clean cuts and tight joints on a pressurized line. A leak at the main is a burst pipe situation.
| Situation | DIY | Hire |
|---|---|---|
| Accessible copper or PEX main with a clear space | Possible | Optional |
| Stuck main shutoff | Risky | Recommended |
| Galvanized or old pipe | Not advised | Recommended |
| Permit needed | Check first | Plumber can handle |
| Need a drain or power, as for a softener | Complex | Recommended |
Maintenance is the real cost
Cartridges clog and expire. A neglected filter can cut flow and, if the media is spent, stop treating the water. Note the replacement interval on a calendar and keep spare cartridges.
A filter also cannot repair old pipes. Rusty water that arrives after the filter is a pipe problem, and repiping is the lasting fix.
Filter types in plain terms
| Type | Targets | Does not do |
|---|---|---|
| Sediment filter | Sand, silt, rust flakes | Chlorine taste or dissolved minerals |
| Carbon filter | Chlorine taste and smell | Scale or most dissolved minerals |
| Reverse osmosis | Many dissolved contaminants, at a single tap | Treat the whole house at a useful flow |
| Softener | Hardness minerals | Filter particles or taste |
| Ultraviolet unit | Microbes | Remove chemicals or particles |
Many systems stack two stages, such as sediment then carbon. The order matters, because the sediment stage protects the carbon stage from clogging.
Mistakes that spoil a DIY filter install
- Buying a filter with a flow rating below your household peak demand, which cuts pressure at the tap.
- Skipping the bypass valves, which makes cartridge changes messy.
- Mounting the housing without room to unscrew it.
- Forgetting to flush new cartridges before use.
- Installing on a pipe with a failing shutoff, so you cannot stop the water.
If you want a filter at the kitchen tap only, an under-sink unit is simpler and cheaper than a whole-house system. It protects drinking water without touching the main line.
A realistic look at time and tools
A competent owner with the right tools can mount a filter housing in an afternoon. The tools include a pipe cutter for the pipe type, deburring tool, wrenches, a level and fittings suited to the pipe. If your main is copper, you may also need a torch and solder, which adds fire risk and skill.
Allow time to shut off water, drain the line and test for leaks. Plan for the household to be without water for a few hours. Have a plan if something goes wrong, such as a stuck valve or a joint that will not seal.
Many people begin as DIY and call a plumber after the first fitting leaks. That is a sensible fallback, as long as you stop before the main line is damaged. A plumber can finish the install and check your work.
Permits and warranty questions
Adding a filter to the main line is a plumbing alteration. Whether it needs a permit depends on the City and the scope, so ask the Building Division before you start. An unpermitted alteration can complicate a home sale or an insurance claim.
Read the filter's warranty too. Some makers require installation by a licensed plumber to keep it valid, and some void it if cartridges are changed late. A short read of the manual before you buy saves an argument later.
What Mountain View and Los Altos water is made of
The City of Mountain View's published reports describe its supply as mostly from the San Francisco Public Utilities Commission, with Valley Water and local groundwater for the rest. The City's water quality page also states its 2024 inventory found no lead service lines. That is about the line from the main, not the pipes inside your house.
Many addresses in Los Altos are served by California Water Service's Los Altos Suburban district, which uses local groundwater and treated imported water. Read your own provider's report for the details. We do not quote a hardness figure.
Our service area page lists the towns where a plumber can take over a filter install that gets stuck.
Cutting into the main water line is plumbing work under the California Plumbing Code, so ask the Building Division what applies to your address before you pick up a pipe cutter.
Questions about this topic
Do I need a whole-house filter in Mountain View?
It depends on your goal. Read your provider's annual report, test your tap and match a filter to what you find.
Does a whole-house filter soften water?
No. A filter and a softener do different jobs. Scale needs conditioning or softening.
Can I install a filter myself?
If the main is accessible and in good shape, many owners can. A stuck valve or old pipe is a reason to hire a plumber.
Does the City say my water has lead?
The City reports no lead service lines in its 2024 inventory. Lead can still come from older fixtures or solder inside a house.
How often should cartridges be changed?
Follow the manufacturer's schedule. Heavy use or poor water shortens it.