manual water pump for boat

Whale brand is reliable and long-lasting. Get a hand pump as it is much easier to operate in rough weather than a foot pump. Position it in the cockpit where someone can wedge themselves in/hold on with one hand whilst operating it with the other. Buy a spares kit at the same time.
Remember that your primary aim is to find the leak/hole and stop it. Ensure you have the equipment for that as the first priority.
Don't get a pump too powerful for your usual crew to operate continuously, women and children can struggle with double-action pumps.
Other options*: find your nearest commercial/fisherman's chandlery. They will normally only stock one or two reliable brands which are the ones the locals have come to trust over the years. Their smallest may be too big for you, but at least you'll have reliable brand names.
Whatever you get must be easy to service (or you won't) and easy to clear a blockage in a hurry.
Take some time to review the wiring runs/battery locations of your boat - it may be possible to rearrange things to minimise the chance of losing your electric pump with water in the boat. Remember that water is likely to slosh up the insides of the hull if you are rolling/heeled in rough weather.
Ensure your sailing routine includes regular checks of the bilges - early detection is half the battle.
Forgive me if any of this is teaching you to suck eggs - you don't give your experience level.
(Experience: 14,000 sea miles, Yachtmaster, singlehanded transatlantic)
*Or buy a catamaran - they can't sink 😉

Thank you oldscool for the info. You really know your stuff.

My mistake, I wasn't clear on what water system I was talking about. It's the tape water (drinking) for in the sinks not for the bilge. So if the batteries are low and no sun for the solar to work we want something that we can hook up or is already hooked up permanent to the water tanks. The size of the sailboat is 36 feet.

Ah, well in the case of a non essential back-up almost anything will do. Save your money and get the cheapest you can find. Try garage sales. Many boats used to have then to feed seawater for washing up to save the fresh, but with watermakers even the long distance types have removed them. You can usually make new seals by cutting up any old rubber/plastic (I've done that in an emergency). Personally I've just used the water from one of the small containers I keep full of fresh, and they can also be grabbed if running for the liferaft. A five litre can or two should work fine for cooking/washing up. Depends how often and for how long you'll think you'll be using it.

25-years ago I saw a neat bilge pump. It was non-powered and operated by the rocking motion of the boat. It was sort of a heavy cam on a flat plate. It would spin easily as the boat rocked at anchor. There was a battery operated pump, too, but this other pump was there and piped separately.

a bucket 😛