I pump water up from in front of my house when it's high tide into a 1500 liter tank outside. I then filter it until it's clear, then let sit until I feel like doing a water change.
For a water change I turn off all pumps, then turn a valve and the water drains out into the earth about 5 feet down outside of the house. Then I turn on the pump from the holding tank which pumps the NSW into the house. All in all it takes about an hour to drain the water ( 1000 liters ) and pump in the new water.
So far I have only had one episode where the water was bad, but it killed off almost all of my fish, except the rarest and most expensive and a local 16 inch tang that I've had from day one. This episode taught me to only pump water when it's a very high tide assuring me that the water is relatively clean. I live in a bay where dive boats go out every day so there is some oil in the water and it accumulates in the well I have dug where I pump the water.