Cloudy water, particles in water, sediment and silt, plugged screens and faucets, damage to appliances and washing machines.
Typically occurs with wells that are in sandy areas or with surface water that may contain a great deal of silt. Turbidity is the cloudiness or haziness of water caused by individual particles that are generally invisible to the naked eye. It can be caused by soil erosion, waste discharge, urban runoff, eroding stream banks, bottom feeding fish and algae growth.
There is probably no health concerns with this (other than grit between your teeth), but it is a nuisance that creates problems throughout the home.
Any level that creates problems.
Removing sand, silt, sediment or turbidity is an inexact science - you simply have to try micron sizes and types of filters in order to remove the above properly. This will give you a good start.