When tied to a dock for an extended period it is really handy to connect the local city water supply to directly to your boat, and bypass the tanks. It is convenient, no running out of water in the middle of a shower, and in our case it also is advantageous that we can keep chlorine out of our main water tank. This is important because we use that water to flush our watermaker’s reverse osmosis membranes which can be destroyed by the chlorine added to most municipal water systems.
There is a potentially serious downside to this plan. Connecting to the dock water like this means we have an essentially infinite high-pressure supply of water coming into your boat. If any hose or fitting was to fail while we were away from the boat, water would keep flowing, possibly overwhelming the bilge pump, and sinking the boat. In my years around boats I personally know of two boats that have sunk at the dock because of a city water connection. Even though this risk might be small, it is not worth taking without figuring out some way to mitigate it.
One solution is to have a convenient valve in the water line that you shut off every time you leave the boat. This is a perfect solution, except for the one fallible part: ME! I forget.
Fortunately, there there is a simple, and unusually affordable, solution: a sprinkler timer. A small device gardeners use to automatically turn off water after a suitable amount has been delivered to their plants. Most of the mechanical ones are not “timers,” they do not count elapsed time, but rather they actually count the volume of water delivered. When the amount of water selected on the dial has been delivered, a valve closes, and the water is shut off.
We set ours for about 200 gallons. If we were away from the boat, and a plumbing failure occurred, that is the maximum amount of water that would be dumped into the hull. Certainly more than we would like, but not enough to create a disaster. With this addition, we feel safe enough to leave dock water connected when we leave the boat for short periods.
The fitting on the hull the hose attaches to incorporates a pressure control valve that reduces city water pressure to 50 PSI, something more typical for boat water systems. The inlet fitting is mounted under our helm seat where it is out of the way, and yet has easy plumbing access to the engine room.