Depends on how you use your boat. The water will go from fresh to stale to putrid as time goes by. But if you entertain, live, and sleep aboard, that water can be pretty convenient for cooking and washing.
Figure the weight is "a pint a pound" or about 8 pounds per gallon.
thanxs for your response ,Where can i find a water guage ?
Cant remember the manufacturer but on "ship shape TV " this weekend they were reviewing a "flow meter" for fresh water tank. Rather than trying to measure the amount of water in the tank it was a flow meter that measure how many gallons have passed through the hose. when you fill your tank reset it and then keep track of how many of the 28 gallons have been used.
found it....probably pricey but I bet it works great
https://birdoff.com/watercounter.php
Several years ago I got rid of the 2 stock 17 gallon fresh water tanks. They were the original and the water that came out of them smelled and tasted nasty. We didn't even like using it to wash dishes or take showers.
I installed 6 pieces of 4"PVC water pipe 10' long. 3 on each side under the floor boards on each side of the fuel tank. I measured the amount in which they hold which comes to about 42 gallons. I have about 8 more gallons than before and with the water tubes below the water line, the boat actually sits higher with the tubes full of water vs how it was with the storage tanks that sat higher in the boat.
When my water gets low, the faucets will spit and sputter and that tells me it is time to go pump out the holding tank and refill my fresh water supply. Usually a full supply will last my wife and I two weekends.
Before I replaced the whole fresh water system, we also used jugs of water. Now that we actually use our fresh water system, it is nice to use the boat as it was intended. Its nice not having water jugs/bottles taking up much needed space.
If your planning on cruising or use for water sports, then you want your tanks empty of course. Less weight = less fuel consumption. If I was going to take a cruise for a long distance, then I would only start out with a half load and refill as needed.
tiger; we have found that we get along fine leaving our tank dry[20 gal x 8#]
this is the same as one more person on board. we carry drinking water which we buy by the gallon and it is always fresh and easy to put in the frig or cooler. we carry about a gallon per person per day and this covers our drinking,cooking,brushing teeth ect. your usage may vary but this work for us
that said we boat on pretty clear lakes and have a raw water shower that we can use to wash down any thing we need,boat, sandy feet, pets, ect.
it is plumbed into the motor so we are able to get hot warm or cold water as needed.
in salt or brackish or muddy water i can see where this wouldnt work and then the tank would see more use
LOWRANCE 49-611 LMF-200 gauges have quite a few different sending units available. i think you can get one that will work in a water tank