[Cindy-Lee]

Hi. I'm a new home owner and I wanted to confirm that this is the main water shutoff valve. As well, do I need to turn the blue knob? If not, what is could the blue one be for? I need to change a moen part in my shower. Do I have to open and close this slowly?

 

[J. V.]

You have 2 valves. Looks like the one on the bottom quit working/failed so instead of removing it, they installed another valve.
Why not turn one off at a time and see?

 

[lenaitch]

It looks like the 2nd (blue) one has a drain nipple on it. They might have added that for that reason (although a simple faucet would have worked better assuming the lower - red - valve still works.

 

[dj3]

Go ahead and try the valves to see which one will stop the water flow.

 

[HitLines]

The blue handled valve is a gate valve and is probably the one that failed (if it has). The red handled valve is a ball valve and is a better type of valve.