We installed a new vanity in our rental unit and the tenants just wrote us that...

since you installed the new vanity and taps in the bathroom, there is little to no water pressure. Some days its no more then a trickle. We thought it would get better on its own but it has been getting worse.

Why would this be, it was working fine when we left.
Type,
Danze Chrome 'Teapot' Bathroom bought at Canadian Tire

We installed a new vanity in our rental unit and the tenants just wrote us that....

since you installed the new vanity and taps in the bathroom, there is little to no water pressure. Some days its no more then a trickle. We thought it would get better on its own but it has been getting worse.

Why would this be, it was working fine when we left.
Type,
Danze Chrome 'Teapot' Bathroom bought at Canadian Tire

It's not the new faucet that you in mstalled. When you installed your vainity you dislodged some crud built up on your pipe walls. It took a little time but the faucet drew it up in side it. Have you advised your tenets to unscrew the aerator from the spout and check and clean the screens. If that don't get it click on backwith the brandname and model of the faucet.
Regards, Tom