Before I built the room around my spa and it was outside I used the garden hose to fill it but I at the same time used one of the waterpowered wading pool vacuums to clean the sand out of the tub. This worked out well since I usually had to add water every 10-12 days or so.
Here's a link to the kind I used.
http://compare.ebay.com/like/400071800288?ltyp=AllFixedPriceItemTypesNow that the tub is inside I use my old waterbed adapter kit to fill the spa from a faucet.