Rainwater for the hoofy ones

[SurelyYoureJokingMrFeynman]

Livestock numpty here, especially wrt UK standards. But is stored rainwater considered suitable drinking water for horses here?

I'm wondering whether to do a two-birds-one-stone job and offer my neighbour the run-off from our house roof, possibly going halves on a tank to store it in the field. It would save me the expense of rebuilding a collapsed rainwater drain.

But the water would end up stored for a long time, as I'd want a tank with good capacity (if it overflowed regularly I'd have to rebuild the drain anyway, to avoid damp issues).

Will I look like an idiot if I suggest this to neighbour?

They can drink rainwater - but personally I wouldn't use it as my main water source for mine... especially if it's been standing a while.

We have a rainwater collection system that takes everything off our stable roofs and holds it in 3 thousand litre tanks , that are then raised on railway sleepers to sit above our hay soaker , and we use it to soak their hay with , and have done for years with no ill effects . It gets used all winter , then emptied and cleaned out when they're out for the summer . It also gets used for the occasional bath , but their drinking water comes from the mains , which is again recycled the following morning into the hay soaker . Saves us a fortune in water .

I've never used anything else.We have several tanks in the farmyard which the gutters run into and have always used this for everything.

Thanks for thoughts.

I've just worked out the average supply would be about 4000 litres a month. Obviously more during long wet spells.

So unless there's some use for at least 4000 l/m, at the wrong end of the field for the stable, I'd need the drain anyway.

(Field currently has three ponies, btw, which I'm told is the comfortable number for it.)