Water, Water everywhere
Different types of water on boats
In catalogues and brochures for new boats the options list can get confusing, especially when it comes to water, the three types of water on board a boat are Fresh (hot and cold), Grey and black, the separation and discharge of the different types on board will be examined here.
Fresh water
Held in a tank, then pumped to the various taps, showers, water heater and sometimes toilets and ice makers. The fresh water system is operated by a pump that pressurizes the fresh system. The tank is filled via a deck filler, the further away a fresh water deck fitting is from the fuel tank fitting the better, it would not be the first time fuel has been put into the fresh water tank and vice versa.
On smaller boats where the turnover of tank filling is quicker than on a large boat there are rarely too many issues, the pumps wear out from time to time and little else. I wouldn't recommend drinking the water from the tank on smaller boats, better to bring it with you, using the water for showering or rinsing things is fine, that said, there are an increasing number of sports boats in the sub 35 foot range that come with a carbon filter to clean the water coming from the tank, you will also find filter systems installed on ice machines, these filters should be considered a maintenance item and changed regularly, if you don´t have one fitted, its a straightforward upgrade.
Large fresh water tanks
A quick look at the specs on a couple of 50 foot planing boats and the tank size is around 500 to 600 litres, then a look at the specs on a ocean going trawler yacht of the same size and the tank size jumps to almost 1200 litres, that's about 1,2 metric tons of water!
Picture the scene, in a berth in a port you´re visiting, just going to fill up or top out the water tank before leaving, an hour later and you are still there, some ports have low water pressure and small diameter hoses so if you have to fill a large tank, factor in the time it will take.
Leaving water in the tanks for a long time can cause it to create some “interesting odours”, I have even seen the mesh filters on the fresh water pumps blocked with the water coming from the tank where it had been sitting for a long time. Additives and purification tablets are readily available for treating the fresh water tanks.
Where fitted, a city water hookup allows a hose to be connected directly from the dock to he boat, no need to be constantly filling up the tank. The fitting is a regulator, it takes the mains water pressure and lowers it to one suitable for use on the boat.
It´s worth mentioning that larger boats with more space can have water makers fitted. These turn sea water into fresh water and send it straight to the fresh water tank.
Grey water
Used for general domestic use such as showering, wash basins and galley or wetbar sinks. In most cases at the time of writing, grey water is discharged mostly straight overboard or a combination of a grey water storage tank or shower box and direct overboard discharges. Direct overboard discharge is a contentious issue due to pollution of the sea from various soaps, shampoos and suchlike. Biodegradable soaps for use on boats and caravans are available. I have been informed that for people who navigate in certain areas new rules are coming into force to prevent grey water from being directly discharged.
Shower boxes are quite common on even small cruiser types boats, the shower drain, basin and sometimes the galley sink and air conditioning condensate drain all flow into the shower box, inside the box is a bilge pump that discharges the water when a specific level is reached, these shower box drains are a form of grey water tank, although they are very small in capacity, only a few litres. There is a filter inside the box to prevent hair and dirt clogging the pump, periodically the box should be cleaned, a sort of “wax” can form in them and lead to odours, they are usually installed in an area where you can access them, under a floor hatch is typical.
On much older boats, shower boxes were not installed and any grey water systems that could not de drained straight overboard just drained into the bilge, a very worthy upgrade is to install one of these boxes, it´s good practice to also install a bilge pump outside of the box in case it overflows, actually its good practice to install a bilge pump in any area where water is likely to accumulate.
Larger boats will often have the grey water option from the factory or it will be a standard fit, I have noticed the Italian boatbuilders are very switched on to this. The tank will be considerably larger than a shower box, the pump is controlled from a panel for automatic or manual operation, so if anchored or navigating through an area where direct discharge is prohibited the pump is switched off, for the most part the pump is left in automatic mode, much like the shower box, when a certain level is reached then the pump will empty the tank. Some larger boats have several grey water tanks and pumps with each one having a gauge that indicated how full the tank is, in really large or digitally connected boats, all this can be seen on electronic screens.
Incidentally, I have seen a couple of boatbuilders quoting grey water tank or grey water installation, what they do is plumb the showerbox into the black water tank, it is a solution but will quickly fill the black water tank.
Black water
This where all the contents of the toilet go into. As you would imagine black water systems have become more common even on small boats (most new open 27 and 28 footers have them installed or are on the options list). The tank is pumped out via pump or macerator (a combined pump and bladed food processor type of thing that breaks everything up) and discharges it overboard.
Some countries and local regions require inspection of boats at regular intervals to ensure than they comply with regulations, typically the black water system comes high on the list, I am informed that in the US the coastguard can board a vessel for inspection and the thru hull discharge fitting must be closed and locked or prohibited in some physical way from being opened so that contents of the tank cannot be discharged where they shouldn't.
Apart from emptying the tank overboard, there should also be a deck (or exterior to the boat) mounted fitting so an external pump and hose can be used to empty the tank. It all sounds revolting, but you don't see anything or smell anything, effluent (the liquid waste from the tank into the sea is somewhat biodegradable), that however does not give you carte blanche to discharge the tank just anywhere, there are rules, the fines are large for illegally discharging the black water tank.
Unlike grey water systems where an automatic mode will switch on the discharge pump, black water systems have no such function, the discharge pump must be manually activated. The better systems will have gauges that indicate the level of the tank and sometimes the flushing cycle of the toilet is stopped when the tank is full.
I have done a few retro installations of black water tanks, macerators and such, the most difficult part is finding the space to mount a tank of adequate size, large boats with multiple heads deal with this by fitting more than one tank, a sort of redundancy in case one toilet or discharge pump should fail. Some boats where the costs made the installation of a black water tank post production too great simply had the toilet removed altogether.
